1024x1024 isn't big enough for skin textures IMO Especially if you want them used in portraits. 2048x2048 is a much better size and gives nice detail on closeup. Also, I'll once again say psd is a good lossless format. You don't sell skin textures with the thought of them being edited (nor clothing textures for that matter) so what your customers owns with regards to paint programs isn't an issue. It'd only be if you were selling merchant resources that this would be a factor.