I'd assumed all along that humanoid AIs did it to appear conventional; Pintsize wears his tie for "dates" as a social convention but clearly doesn't feel the need to wear anything.
The Idoru staff wear quasi-uniform clothing to indicate job status and indicate that "human" social conventions should be employed when interacting with them. Whether Momo really has any actual anatomical details, who knows but certainly if she walked around "uncovered" that would be tantamount to saying "I'm a machine not covered by human conventions".
May's orange suit is a prison uniform, then. This suggests in turn that she had no clothes to return on release and hence, wasn't previously humanoid, or maybe effects are returned to the original owner or sold, who knows. I'd guess that the "hundred bucks for essentials" is for transport; AIs don't eat and are capable of walking but that's not always a good way to get about, too slow. Presumably they need recharging in some way? That won't be free. They have internet capability and therefore, presumably have data charges if using public networks.
Momo was referred to as having "needs" as a throw-away joke on a couple of occasions, but AIs have needs in a literal sense, too