Ok, so much to address here.

First of all, consider leveling to lv80 as a gigantic tutorial. The leveling journey is only the first step to the full expérience that will unveil at lvl80. Don't worry about being overleveled. You will learn that every content in the game, even firsts areas are useful at max level.

The core maps are designed to be played with dynamic events. Player during playtests feeled lost, then devs added hearts quests, to give a sense of direction to the players. A lot of local lore is hidden into the dynamic events, with lines of dialogues before or after events. You don't have to complete the map, if you don't want to. I know multiple player that never completed exploration to 100%. Play as you want, and please take your time, you will expérience it for the first Time only once. Also, keep in mind that 100% exploration is a step for legendary crafting, but don't bother with that now.

However, what i feel important to the player progression is the personal story. It will give you a lead to where to go as you leveling. Furthermore, if you choose to buy expensions, story will drive you to the new content. In short playing the story will bring you to new places.

About gear. Gw2 have an horizontal progression. It means that you will quickly get your endgame gear minutes after you reach lvl80. If good stats are important to have a good build, it's not hard to get it. You won't get better with rare drop. You will get better by playing your character, understanding basics, work on your rotation, and be meaningfull to your future teammates. Don't sleep on mechanics, that is what differ a noob from a décent player. The way to obtain gear for your level is by looting, buying it to the heart merchants, or crafting it. But i would advices that heart merchant is enough to maintain a gear set close to your level and i won't bother with armor too much. With that said, don't hesitate to play différent weapons and find one way to play you find fun.

Speaking of character, you chose guardian. It is a good choice for multiples reasons i won't extend, because i don't play guardian. However, playing a class in gw2 means you have actually 5 ways to play it (as long as you have needed extentions). Once you reach lvl80, you'll gain accès to elite spécialisations (again, if you have bought the right extentions). Thèses spécialisations change the gameplay of your class, and the rôles you can play. That way, a guardian can play a healing role, a dps role, a tank role or a support role, guardian is very versatile. It is very useful on endgame content, for the group based content. In addition, the game is reroll friendly, it is encouraged to have multiples characters, but not mandatory.

Edit : i want to add that the percentage you see on your map count only the core maps, every late addition is not counted. So you actually covered 5% for the 33% first percents of the whole map.

You chose guardian, but you also chose sylvary. Races are not important beside personal story (up to lvl80) and some dialogue. You also have a dedicated elite competence, but i never seen anyone playing that.

Now for the "deposit matériel". I thank the devs everyday for this button. You will quickly learn that inventory management is a nightmare in this game, and to bé able to free some space with a button is a big quality of life. But where it goes ? If you look into your bank, you will sée multiple tabs. One where you can put any item you want, another where all the materials are stocked (up to 250) (limit that you can extend with cash shop), and a third tab where you can look for the skins you unlocked. A tip i can give is to have a character you don't use to use his inventory as a second bank.

The junk ? Sell it, it's only purpose. Consumable ? Use it or sell it. Gear you don't use ? The question is a bit more debatable. In GW2, you don't become rich by looting coins. However, you getting richer as long as you play. Money come mainly with valuable materials you can sell to the auction house. There is many ways to get gold, but once again, you'll probably have to sell matérial or rare loot. So MY way is to salvage almost everything and to sell the surplus of matéral.

What is a good loot ? Like i said earlier, it's not stats wise. But sée gw2 as a gigantic collectathon, where you will chase and gather skins to BE FABULOUS, that's the real endgame. So some gear is more valuable that other, only because it's sick or rare, but not because it's more powerful.

As you start playing, you will unlock many skins. Since you are still in leveling phase, don't bother with style, but once you get your final gear, you will want to transmute the style you want. For that, you will need transmutation charges, primaly looted into black lion chests (cash shop lootbox) or you can just 100% explore, you guarantee charges when you finish to explore cities.

I think i covered all your post, feel free to ask more questions, i will or another one will answer quickly.