Really depends on whether you intend to mix in the same space as record. Room problems (standing waves, early reflections) occur in most household rooms that would make your monitors less "truthful" and make it hard to do mixes that translate well in other places!
Adding channels via ADAT is an effective way of expanding your kit to record drums - i recently purchased Audient ASP800 for this very reason, and connect it via ADAT whenever I need more channels than my RME's have.
I guess you should be careful about whether you are trying to optimise the space for recording, or mixing. Fashion nowadays is to record as dry as possible - which can be helped by doing things like hanging up duvets behind the singer. lots of good advice in Sound on Sound articles. That may work for a corner of your "mixing room", but an entirely different approach / new set of compromises may be needed if you want to record drums in the same space as you mix / monitor. Drums normally sound best in a good room, so making it completely "dead" is unlikely to get great results IMO...
It is definitely a journey, so take your time, experiment, and try to understand some of the physics underlying what's happening - then you can address problems as you become more and more aware of them. I guess I'm saying that you shouldn't expect to have a great sounding space with perfect results straight away - but don't get discouraged! It's definitely a hugely complex area - with the key pothole being that you can easily sink lots and lots of money into things that make objectively little difference to the results.
Studio gear GAS is even more dangerous than bass/guitar GAS, in my experience... you've been warned!