Angus and Marigold/Momo share a two bedroom apartment. We are not sure how Momo lives, but the best guess is that she sleeps (or sits) in Marigold's room, or on the couch. Also, Momo has said she wanted more room to herself. Momo has a similar job as Marten at the library, which probably means she has about the same income as him. If Marten can afford to pay his rent, so should Momo, especially since she has no food and beer expences (but perhaps a higher electricity bill). Momo is probably paying Marigold back for her Idoru upgrade, but we have no idea how much.
Dale and May moving in would be a terrible idea. This would mean May and Momo would have to share a room, and that would never work. Also, Dale would quickly tire of Marigold's sloppy housekeeping; Marigold would be edgy around May, and angry at Dale for supporting May. The apartment's bandwidth would be too small for their combined gaming activities, and they would quickly become gaming enemies again. Unless Jeph wants a quick breakup, this should not happen.