Sounds like fun! I don't think you're asking for trouble--we all have to start somewhere, and ducks are not that much work once fully grown, although you do need to be able to empty swimming water containers unless they'll have a full-blown pond (either a large natural pond or a well-filtered manufactured pond--if the latter, then do your research because filtration is complicated with something as messy as waterfowl involved). I only mention that because you mentioned your age, and sometimes back trouble comes with that. There are ways around lifting water containers, but many of us simply use kiddie pools and empty them regularly. The more ducks you have, the more water you'll need.
As for your questions: Yes, the ducks *will* cross breed unless you keep them physically separated. Additionally, the Golden 300's are a hybrid and will not breed true (i.e., their offspring will not be Golden 300s).
Some people keep ducks in pairs, but most consider larger groups of 3-6 females per male to be a better combination. If you want to breed the ducks, you would probably be better off starting with one or two breeds--trying to keep several breeds separated is going to be a really huge hassle unless you already have the set-up for it. Of course, there is nothing wrong with breeding mutt ducks either, if that's what you want.
If you want to read more, the best overall guide for raising ducks is Dave Holderread's Storey's Guide to Raising Ducks, and his waterfowl farm (
www.holderreadfarm.com) is an awesome place to order ducklings when you're ready--but order ahead, because they sell out by Spring!
Good luck!
