In terms of hats and misc, as was said above, they'll come with time. if you don't have all of the class weapons, however, they'll also come through random drops, OR, you can complete the achievements of the various classes to get a guaranteed copy of each of their unlockable weapons (with a few notable exceptions, namely the soldier's gunboats and all community weapons, which can be crafted using the other, regular weapons).
As for starting class, it comes down to what your previous game playing experience is. I see you're from CS:S, so you might find some comfort with the sniper. It's a nice and easy concept to get behind in the beginning. However, as I said in the thread Quaffer recommended (which you should read) you should play medic. As a medic, you have to pair up with people to be the most successful you can be; this means that you'll always have a heavy, soldier, pyro or demo kicking around to observe.
As for what NOT to start with: spy. The spy, I don't find, anyhow, is really a beginner's class. The difference between a good spy and a bad spy are extremely obvious.
However, what you should really do is stop listening to all that advice for now, and just play the game. After you get a better sense for what you're doing, then you can seek out the class guides and the community asking for tips on x class.
As for maps, you might be able to download it from fpsbanana.com. However, I would recommend not starting on mesa; a lot of really good players play there, and even more than good players, there are players who really know how to exploit the map (in a good, non-malicious way) and will hand you your butt if you don't know what you're doing. What I would suggest is going to insta-respawn 2fort. it's often full, great opportunity to snipe, and there will always be a good mix of veterans AND people who are much worse than you. That's where I learned to play back in the day, and I heartily recommend it to any beginner.
You can add me on steam and we can talk, if you like, although I don't actually have steam at the moment what with my computer dying a little while ago. That's something I might just fix today though.
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