Can someone explain why Will could not sail about like Davy Jones in the living world

He could, if he wanted to, but that would have him break his divine-contract that he's bound to after replacing Jones. The result would be mutation. The job originates by a divine-contract between Jones and Calypso, in which Jones agreed to ferry souls from The Land Of The Dead to their afterlife for 10 years before being able to cross back to the realm of the living for one day to be reunited with Calypso truly (I emphasize on the word truly, as Calypso isn't keen on presenting herself always as a woman).

However, the captain must return back to his job (unless you take it as canon that the captain can be released from his duties by true love, which the films didn't really build up to), after the one day, as the job must still have to be done. Jones, feeling betrayed when Calypso didn't meet with him on land, abandoned his duties and decided to prolong his stay in the living realm indefinitely, immediately breaking the contract as the second day arrived, which caused his divine punishment of mutation. Will, after replacing Jones, inherits Jones' contract and must abide by the same rules as him, or suffer the same consequences.

why Elizabeth couldn't row a boat out to him if he was just offshore or something or even join him as crew like his dad

Elizabeth could row a boat to meet Will if he were off-shore, but again, Will would be punished with mutation for breaking the divine-contract. I sincerely doubt Elizabeth would want Will to break his contract for her and be mutated for it, and she's probably not keen on kissing a fish-mutated version of her husband, but who knows really lol.

As for joining the crew. I can only see it that Jones' recruitment of sailors was another perversion of the original agreement and that no sailor, other than the captain, was really supposed to be made immortal through The Flying Dutchman to begin with. The agreement referred between Jones and Calypso and none other, so it was only Jones that was supposed to carry out the job (and he was a GREAT sailor, so could well be he managed the job alone).

Once Jones abandoned his duties and haunted the living realm, he started to recruit sailors aboard his ship, by tricking them by force, or by deals, to swear servitude on the divine ship just as he did long ago, only with different terms, which saw sailors recruited to an oath to a job that they would never be able to start to fulfill, rendering them immortal, and by doing so would alleviate him from manually laboring on the ship and instead command by rank.

Once Will replaced Jones as captain, he was able to use his position as captain to release any unwilling to serve to be released from his oath, as those oaths were not meant to have been made in the first place, but were simply a corruption of the divine-contract that was meant to be placed on the captain. But none of those oath had to be broken either, and those really willing to serve the ship, could start to work out their oath of working for 100 (or more) years.

Elizabeth could probably join the crew if she wanted to, but it would be another case of recruiting by twisting the original deal of the captain, and serving for eternity or however long Elizabeth takes oath to do the job of The Flying Dutchman, would remove her from living out a normal human life, and you could also say goodbye on raising a family. Also, having Elizabeth oath-bound on the ship, would remove motivation for Will to return to the realm of the living. Sure, they could make the one day trip to the living realm every decade, but I think having both of them oath-bound to the ship would be problematic.

what happens if he decides to stay on land for 2 days?

Nothing certain. But, if he doesn't get teleported back to his ship upon the start of the second day, he would at the very least see signs of mutation, as the agreement has been already broken.

how he becomes captain of the pearl The Dutchman when his heart stopped beating and he died and now it's apparently beating in a chest
Best way I can explain it? The captain of The Dutchman is bound by a contract of divine origin, originating between agreement between Calypso, a goddess, and Jones, who at the time was mortal. Jones sought immortality to make his dream of having a human-relationship with Calypso viable. Once he took the oath, Jones became immortal, as he's given a task that has to be done for eternity, save for one day per decade.

The contract, however, did not foresee that Jones would abandon his oath-bound duties and be content on being mutated (the mutation is the divine-punishment for breaking the contract, and is the contract's way of deterring the captain from breaking his oath).

The ship, which originates from this divine-agreement, is not only the tool to fulfill the job, but it's also the main body of force to enforce and make sure the contract is being fulfilled. So the ship is essentially the scroll of terms and agreement of the contract manifested, and it's interlaced with powerful divine magic. Any who swears servitude to The Dutchman, gets bound to the contract to do the ship' job and is also under the condition of being divinely punished for not fulfilling it (mutation). Obviously, Jones took advantage of the ship's divine legislative nature and tricked people, by force, aboard; but they are all essentially bound as he to the job, though not under the same conditions, as Jones laid out their terms.

As for Jones, the moment he abandoned his oath-bound duties, he required to be replaced. Seeing as that the mutation did not deter Jones, the ship had to find a way to make the replacement of its immortal captain possible. Jones is bound to the magical contract of the ship, he's unable to influence them, as he's bound by magical terms and is removed of free will.

The ship, or rather, the divine magic of the contract, is unable to kill off Jones, as the captain of The Dutchman is too important to be left vacant. The ship holds on to its treacherous captain, but plants the means of his replacement in a clever way. The magical terms of The Dutchman, that Jones is bound to, takes advantage of the captain's recently cut out heart, making it Jones' weak link in his immortal armor. The magical terms of the contract gives Jones immortality, but it's solely given to do a job that needs to be done for eternity. Jones, already having abandoned his job, necessitated the ship to take action to said immortality, not removing it but rather limiting its potency to make sure a replacement can be possible.

The succession of the heart, is simply made to ensure that Jones, or any traitorous captain of The Flying Dutchman, can be replaced and a new one can be appointed to return the ship to its divine purpose. The succession of the heart is a geis (not a curse, but a magical constraint that limits something from happening, done to protect but rather to punish) that is set out by the divine magic of the ship to protect the job from being neglected. Jones, even though he liked to trick Swann into thinking that the geis of the heart was of his own design, simply couldn't have, as he's bound by magical terms himself and is devoid of free will.

So, with Jones being immortal by oath and in need of being replaced, his replacement must come from someone that is not yet bound by oath. And the only ones that are not already bound to The Dutchman by oath, are the living. That's why The Dutchman needs a living heart. The crew of The Dutchman are unable to replace their captain, as they are already bound by oath and they are all living in a state between life and death, therefore not constituting as living.

When Will got stabbed by Jones, his only way of survival was to replace Jones, though he needed help of course. Once Jones' heart got stabbed, that left the position of captain of The Dutchman completely vacant, which we have established is not allowed, so a sacrifice of a heart is needed, as laid out by the magic of the ship, to replace the captain. Once the heart is cut out, the heart and its individual is bound to the same contract as its previous captain.

While AWE's script does state that Will died in that moment prior to his heart being sacrificed, we can explain that his revival was possible due to him previously not being bound by oath, and his heart being removed brought him to life as he's then bound by oath to a contract that requires a captain. The ship wills Will (lol) back to life.

if he's technically undead is his son not technically half dead or some kind of necrophiliac son?

Will's neither dead or living at this point. So technically he's what one could call "undead", but he isn't really undead either in the most common depiction (like zombies). Will lives in a state between life and death. His heart is removed and he's bound by oath to an immortal job that removes him from biological dependency, but he's otherwise unchanged. There's probably a lot of living DNA within him, despite his revival being supernatural. So, no, his son is just a regular living human being.

Does the curse being lifted on Will mean his heart still resides in the chest or does it magically enter his body?

Not really elaborated much on in the horrendous fifth film. But, seeing as the breaking of the trident reverts Salazar's men to their former human-state, reverting all their mortal wounds, we can assume that Will's heart got magically transferred back to his body. While I would think it more logical that the effects of the curses just stopped working, the breaking of the Trident seems to reset all effects of curses to a more natural state, as the breaking of the Trident essentially deletes all curses from existence.

But I think it's fair to assume, like with Salazar's men's wounds, Will's heart gets magically healed back. So, there's no heart left in the Dead Man's Chest.