It installs on the side of the helmet only, and the speakers are placed in the ear cut outs in your helmet. I have not noticed wind noise from the unit on the helmet.
If I were you, I'd find a friend who wants one too and go in on a pair(multiset) together. When you buy the pair, you get the version which has the MP3 input that you're looking for, plus it has larger speakers. If you don't buy the multiset but still want the input, you'd have to buy the upgrade for an additional $40(which I ended up doing).
The multiset can be found for $300, when the average price on the single Q2 is around $200.
Make sure the one you buy has the MP3 input!! Otherwise you're going to have to spend another $40 a unit.
If you ride with a friend, it will make riding twice as fun!