Need a battery to start my Onan, 460 cca min, dual-purpose?

You might consider using a deep cycle battery for the house which is generally preferred. Or a marine deep cycle which is a compromised starting battery. Deep cycle batteries will start a gen, but they do cost more being a better battery.

There are various reasons on which bank and batteries to use. Based on what you've posted I'd suggest doing what is easiest and best for you to start as you can make changes down the road as desired. Flooded batteries seem to be the best short term and lowest cost for you.