The short of it is that textures are a costly resource, so your goal should be to get the most out of your textures while keeping them as minimal as possible, both in size and quantity. Stay away from formats which are fat or lossy, and if you need alpha transparency, make sure the format supports it in the way you want.
Separate the process of creating, testing, and compressing your assets. Don't try to reduce your work by flouting common practice, you will almost certainly end up increasing your work and or making the task impossible. A good starting place is using png, gif, or a propriety format developed specifically for whatever your use case is (assuming your use case demands it, though it seems unlikely).
If you're still interested in the subject I advise reading some books/papers/blogs (in that order) on the subject of asset creation for viz-sim and games.