Welcome to MobileRead!
As dwanthny said, calibre does all its conversions entirely standalone. You don't need to keep a stable of ebook devices around! Just batch-convert your books to whatever format(s) you need. I'd go a step beyond his suggestion of testing them with the various desktop viewers, though, and say you should find someone with each of your target devices who could test out the books for you. Check around here -- I'm sure you could find someone with a Kindle, for example, who would be more than happy to read a book and tell you if the formatting is broken. Given the level of quality found in entirely too many commercial ebooks, developing a reputation as a perfectionist would be a good thing.
Feel free to ask questions. We were all new once.