Hi, Marianne. 
On the Stardock website, only support for W10 is noted. Before purchasing, write to Support with your question here: https://esupport.stardock.com/index.php?/Tickets/Submit
Keep the auto reply, and don't answer it. Support works M-F, 9-5 US Eastern time. Currently they they are on summer break. Either a support person will see your question here, or you'll have to wait a week until they reurn...and by then there might be a bit of a backlog.
No, there are free skins still available. It's pretty up to each individual Master whether he/she makes any one skin "paid" or "free".