Has nothing to do with Subeta, see here. Has nothing to do with Subeta really-- which is why I was wondering if such a thing is allowed? And if so, where would I advertise?

So you're selling character designs with complete ref sheets? Or just ref sheets? Anyway, yes, selling for USD is allowed but you must have a sP slot as well. As for the advertising, the Art Market would be the place.

Good luck!

Character designs with reference sheets. Like selling the character here along with the reference sheet for USD (or sP). Also, would having people bid on it in USD be allowed?

theres a rules topic stickied in the art market forum

http://subeta.net/forums/view/430737

as well as a sticked topic of helpful threads in the art market forum