Guild Wars 2

If each crafting profession only gives 10 level for maxing it at 400 ( some are 500 but its not important )

Assuming I’m level 50 now , I only need to max 3 profession to reach 80 and thats it?

I can max another 5 profession on a new character?

If i need to make items , I just have to switch between characters to make em eh?

First of all, you get 10 lvls for crafting from 0-500, so you get around 8 levels for crafting to 0-400, so maxing 3 professions to 400 wil get you from lvl 50 to around 74.

Potentially , you can max all 8 crafts on each of your character and will always get exp for it, it doesnt matter, if you already maxed it on another character.
The Achievement points you get for reaching certain lvls in a craft however, will only be awarded to you once, as achievements are account bound.

You can only have 2 professions active on one character but you can switch the active ones out as often as you like and you wont loose your progress on the deactivated profession.

However, the first time you learn a craft, it doesnt cost anything. But if you want to activate a profession for the 2nd time, it will cost you 40 silver.

If you want to craft something to be used on another character, you have to place the item in your personal bank, so the other character can pick it up, mailing it doesnt work.