You can use any free letter you want. For example, C, couldn't be used, obviously. My three hard drives are C, D, and E. My optical drive is F. Then I have a huge gap separating the rest. As I said, M, N, O, and P, are my card reader, and S, U, and Z are network drives. Drives that allow it, like hard drives, get names, like my C drive is SYSTEM, D is STORAGE, and E is MEDIA. The network drives are recognizable by path. There's very little to memorize, and it sounds like you are over-thinking or over-complicating your setup.