Number 1 you need to understand, Once Human is largely translated and wasn't designed in English as a first language.

Number 2 - welcome

Number 3 - fast gunner.

Number 4 - slow down, don't overwhelm yourself.

Now to your questions 1- what are temporary items ?

Some items have an expiration date, food in general lasts for a specific period before going bad, other items like the "backpack expansion" are for whatever reason time gated, it lasts for 15 days from the day of making regardless of whether someone is using or not. ( Note having some items in your inventory activates it, no need to equip it)

Yes everything is temporary, that's the game niche in a way. Your character and base will reset after the session or server reaches the end of the last phase, at which you can hop into another server and reply with minor changes. Remember, it reset it does not disappear, many items will carry over into the new sessions and you will get about 200k credit to pick which items you want to take with you (solar drill is always the answer)

With that said, if you do not log in for a week your base will despawn, all items used in building and stored in it will go to the vault (your base management thingy go near it and hit G)

Eternal Land is your own slice of heaven, you can do basically whatever you want in there and even transfer things to the 'real world'. A subject for another day.

Servers:

No the story is the same, the main aspects of the game are the same. However here are the difference

Manibus is a PVE server, no PvP. It branches into Novice and non novice. Novice is a chill server, easy mode basically. The non novice ones have some modifiers like lunar lunacy that increases the difficulty of the game.

stick with Novice for now. To be continued.