I'm not sure of the differences between the 900 and the 900a but the 901 doesn't have wifi out of the box but the driver in rpmfusion works well.
Realtek 802.11n chip?
Something like that. Its something like the rt2860 driver. I think it has crappy stuff like stuff in /etc
That's the one. Supposedly the driver is under a rewrite to be included in the upstream kernel, but I am not aware about the current status.
Its been in a rewrite state for ages with what seems like no real progress. I read somewhere the USB variant would be done first but that hasn't seemed to materialise yet.
Peter