I have used a large air compressor and foam filters to run my rooms, I think it is the most cost effective way to filter tank and you can adjust the amount with taps depending on what type of fish you are keeping. Heating the room can be effective, but makes it hard to work in there for to long, I would suggest heating your tanks if you are not going to insulate your garage. A dehumidifier would also be a key/essential piece of equipment IMO. Good luck, I look forward to seeing your set up progress.