Hi, zebra! Glad to see you are from my beloved Boston, where I spent four amazing college years. Just like you, I moved in January (fifteen years ago next January) and was thinking about getting a bike and ride around town (something I finally didn't do and truly regret now).
I don't think you should bother bringing your bike. You can get a good one here cheap. If you plan to use it in town only (no mountain trips), a US$300 mountain bike will do the job perfectly well. IMHO, playera bikes are not good for Buenos Aires. In fact, I think they are dangerous. Hard to maneuver in heavy traffic and they come with coaster brakes, which I find tricky and unreliable for big city riding.
The only thing I'd bring if I were you is a good helmet (assuming you have one). Of course you can get one here too, but as a biker I know that certain equipment is very personal and if you already have a helmet you trust, bring it with you. It want take much space in your luggage anyway.
Any questions about town, traffic, safety, where to go and especially where NOT to go, just PM me. I'd love to join you in your rides, but I sold my last bike some time ago and I'm not planning to get a new one for the time being (I didn't sell my Cratoni helmet, though, and I never will), but I'd be more than glad to assist you in any way possible so don't doubt contacting me.
There are SO many good things about having a bike in this city. Just be forewarned that you shouldn't really leave your bike locked up outside after dark for long (more than an hour or two). If you're going to a friend's house, etc., try to bring it inside. It's better to cart it up a few flights of stairs than have to buy a new one.
