About the tail alpha, just do whatever you want with it. Of course, at the typical game zoom level, you can probably barely even tell that there is a tail. When I make these models, I'm thinking about the reuseability in other games as well (as well as a bit of future-proofing), so I go for a level of detail that is probably unnecessary for normal gameplay. The models are also used in promotional material. So, you don't actually need to paint it at final texture resolution. Textures are so easy to resize afterwards (of course, don't spend a huge amount of time redoing anything now, just for the future I think these are good ideas). Computers are only getting faster, so, it won't take long until that texture size is beefed up a bit. Probably!