I'm playing with Salvinia minima, at least I think it is in my scape, could be natans. How big are the leaves in your Salvinia species? Mine are at about a quarter inch or less. Azolla might be pretty. Frogbit is an option, but this can get big. If you trim the large plants and keep the small, that might be pretty, very large roots, though. Right now, I'm letting my Salvinia go everywhere since I don't have a lot, but as soon as it becomes a problem, I'll contain the growth to plastic rings I make from plastic cups. You get the benefit of floating plants and they don't get everywhere. Other floaters I think would get too big.
Waterchanges. Well, you're going to dose ferts and inject CO2, so you're looking at 50% weekly, at least. Right now, my tank is very new, so I err on caution and do a 50% multiple times a week, especially to remove decaying plant material (read crypt melt) and other items that could lead to ammonia spikes and algae production. This will be a problem in the beginning as several of the plants you've selected will probably convert from emersed to submerged growth. The emerged leaves die and it can get icky. Crypts also melt, so be prepared for that as well.