Hello Escala,
Welcome to Feralhearts!
Its Awesome to meet another Fox Roleplayer. I also Play as a Fox called Swiftpaw
As for your questions about slowing down your Mac, I think it all depends on how old it is. I Use a Mac as well as a PC and the Game runs Great on both of them.
You can't pick pelt textures. But you will be able to customize the colours, and Body.
If at all you get stuck of need any Help, Please feel free to ask. Everyone here is really friendly and helpful.
I hope your time with us will be a enjoyable one. I look forward to seeing you both around the game and the Forums.
All The Best
Medic