Hi Jacks
Currently we support piB+, or pi2b, our recommendation at the moment is pi2b, this allows mode c detection and audio.
Regarding back powering through USB, please be advised this will not start the unit to boot, power must be applied via the micro usb for startup, lots of articles online to explain this
Regarding the micro sd card, minimum 4gb, for all other requirements refer to rasbperry pi foundation articles
Thx
Lee