I'm also new to FF14 and so far I'm enjoying it! Anyway to answer some of your questions:
1) You can check out what 2.0 is all about here: http://lodestone.finalfantasyxiv.com/pl/teaser/
Version 2.0 is what some people also call the console version. It's Square's way of trying to make FF14 work for the PS3 while implementing huge changes to the current game to diminish / remove some of the major issues that plagued the game at launch.
2) The leveling system in FF14 is the same as any other RPG out there -- you gain XP by killing mobs / doing quests and as you gain XP, you gain levels. There are a lot of classes to choose from and from what I know, each class has their own respective level. I can see that you currently have a level 1 THM. If you level one class, only that class will gain a level up meaning all of your other classes will still be at the level that you left them. One of the benefits of leveling up other classes is the ability to include none specific spells to your current class i.e. a THM that can cast cure or a CNJ that can cast lightning etc.
When you die, you need to select the return option via the main menu. This will teleport you to your home point. You will get a debuff for a few minutes reducing your stats for a certain percentage but that shouldn't be much of a problem. I don't think there's any XP loss if you die, but I'm not sure about this. No you will not get a level down if you die, that's for sure.
3) What do you mean trade system? If you mean the ability to trade items with other players, then yes it's possible. There's no main way to sell items like the auction house in WoW, but the community's hoping that one will be implemented in the future.
4) Again do not take word on this since I'm not sure but AFAIK it's currently impossible to use add ons although they're planning on implementing that feature. You can stop the auto hide of your spell bars by going to the main menu > configuration > System > Action bar display to ON.
Good luck and have fun. If you have more questions feel free to ask. If I made any mistakes, I'm imploring the vets to correct them.