First of all, don't become obsessed with obtaining all the items. Learn to become familiar with the basic loadouts of each class, as it will give you a better idea of the role that class plays. Besides, the new weapons are (mostly) sidegrades, not upgrades. A skilled player with a vanilla loadout will beat an unskilled player that's using unlockables nearly every time. As for hats, they serve no practical purpose whatsoever (except for the four Polycount hats that provide minor stat bonuses with certain loadouts, but the user feedback was so caustic that Valve stated they would never do something like that again).
Lilani said:
The best class to start with is Medic. You'll be able to be useful while sitting back and watching how other classes work before trying them, allowing you to become familiar with how things work. Also as Medic, regardless of whether you're FTP or not, people will love you simply because you are a Medic. Just be patient though, there are still some jerks who hate the "FTP newbs" so you might have to deal with some crap there.
Sound advice. I'd also suggest playing Soldier, as he's fairly straightforward and accessible to newcomers. Just make sure to "lead" your targets a bit with your rockets and aim for their feet.
Ever since the game went F2P, there's been an increase in hackers. They still aren't very common (I run into one approximately once every two months or so), but there's definitely more of them out there. If you run across a hacker, just leave the server and find another one. You can take solace that VAC will ban them eventually.
Try to find a few good populated servers and stick with them. I myself prefer ones with 24 player slots and stock map rotations. I despise servers that have tons of custom skins/models/sounds, 32 player slots (way too chaotic and spammy), instant respawns, single map servers, and special bonuses for donators. When in doubt, try letting the matchmaking system find a game for you via the "Play Now" button. It will usually take you to an official Valve server.
Finally, try to keep any possible trading restricted to trading servers. Few things irk me more than players who go to normal servers to spam trade requests, stand in spawn, and generally be a waste of a player slot. Just make sure not to frequent trading servers too often. Dealing with chronic traders can be a frightening experience, what with their obsession with placing arbitrary "prices" on everything. Just get in, make your trade, and get the hell out.