Nothing happens, that information is saved to the steam servers.
In other words they'll be there when you re-install
No, they will not. Only in the event of out-game idling would they do that.
Nope, everything on your profile for TF2 (backpack/controls etc...) is kept online.
You can either delete items, craft weapons together, or buy a backpack expander/ get premium
You can't but it would be cool if you could
You can't, but you can delete all your Achievements and start over.
No. You can only gift the items themselves.
You either buy them from the TF2 catalog or you get them in random drops. So far there haven't been any way to get them for free, aside from trading and finding them.
They are designing a "training" mode for each class.
The "richest" player in TF2 is Bobsplosion: backpack.tf/profiles/76561198027097747?time=1462147200 However, as of May 1, he has moved all of his items to a private account so that he wouldn't be bothered.
No, since your achievements are stored inside Steam Cloud, otherwise people could just edit the relevant file(s) to get all the achievements.
no, the items were only available for pre-release of AC:R. You can craft the items in game. Blueprints can be found on the tf2 wiki
The drop system randomly gives the player an item when playing. In the 10 first hours of you playing, you can get up to 12 items. Every week, the drop system is reset, and happens on Thursday. This means that you can get 12 items every week if you're really lucky.