IDE
this is somewhat strange. Fit-PC have SATA connectors. Maybe you have IDE emulation enabled? If yes, can you try switching SATA mode in BIOS (if it’s possible) to AHCI / SATA instead of IDE?
And about wireless, check This page.
Using USB WiFi adapters is not common practice here, so it may be pretty problematic. Although i had some usb atheros working with my RB.
The IDE to SATA interface is difficult to deal with. With Linux you need to build a driver for it which is not in kernel.
The wifi is Ralink RT2870 but you can use the drivers for RT3180. It works fine, but probably not supported in MT. You can replace it with a usb only miniPCIe or USB module.