If you're hatching them in an incubator, not under a broody hen, and aiming to raise them yourself in a brooder, I'd suggest not starting with ducks. I don't know much about guineas, but I've hatched and raised both chicks and ducklings, and the ducklings are about ten times more work to keep their brooder clean and dry cause they love scooping their drinking water all over the place and paddling in it. They're ridiculously messy. Brooding chicks is dead easy in comparison. As for hatching, chicks might be more sensible to start with too, as they only take 21 days compared with 28 for ducks (35 for muscovys!) and 26-28 for guineas. So, if you don't get it right first time, you're not wasting as much time on each failed hatch till you do get it right. That might sound like a gloomy prediction, but of course you could also have a great hatch first time round. Just thinking out loud...