You have some very good advice here. This was fun to read. The best things I can recommend is to invest some DIY into some gobos to deal with the room. IMO, your goal won't be to treat the room, but to create a tracking area so you can minimize the sound of the room. Some moving blankets draped over mic stands can help, but won't replace the 703 absorbers. Using both can accomplish a lot. I think mics and absorbers will make a bigger difference than upgrading the focusrite. You may consider keeping it and AB'ing against the RME and see if you feel it is worth the extra cost.