I'm not sure but for whatever I combine, if it fits into a flat rate envelope & that's cheaper than by weight I would send that way. 2 yards would easily fit into that. So I'll guestimate 6 but possibly less.
Never heard of them. I did once get a Godzilla Toile from Spoonflower but they are also quite pricey. Pity...they have amazing prints available but at $17ish a yard I can't make any money for the time I put into a dress so I cannot afford to have a shopping spree there.