I read of so many people handwringing over which AI/mixer/card/mics to drop their wedge on, terrified of making a "mistake". Don't worry, there will always be some armpit who says "You haven't bought one of THOSE have you!?"
A modest usb AI,I am a fan of the Emu 0404usb 2.0 but the Novation Nio has caught my attention lately, bit guitar oriented but you can put reverb on the monitor feed, should please the missus!
You say you have a dedicatable room (is that a proper word?)? These days it is very easy to run the recording kit by remote, Tanzport, cheap video kit. You could treat the room in the best way for recording and maybe set the "kit" up elsewhere? Much depends of course on the sort of music you are going to be doing.
Download manuals of AI's and mixers etc. These usually give hookup diagrams and signal flow block diagrams and help you get your head around the nuts and bolts.
But yes. Get something simple (a £50 mixer will NEVER be out of use, if only as a talkback system!)and get stuck in!