hi cindy
in my opinion, buttons don't smell, i can totally vouch for them LOL! this is a bit gross (and maybe too much information) but their poop is just different from finch/canary poop. their poop is larger and solid, and it can build up if its not cleaned regularly (just like any other animal). also, i find that certain foods make their poop smell bad... so i steer clear of freeze dried bloodworms now, as i found that this was what made it really smelly.
also, regarding your concern about having finches hanging out on the floor with the quail, i have a button that lives in a community cage full of little waxbills, and often i see my gold breast pair cuddling up with her on the floor! as well, in my other community cage, i have another button who sits very comfortably and calmly with my shaft tails and societies who love to sit on the ground. so in my opinion, its not a problem at all! additionally, all of my buttons share food containers with the finches, and there is never any fighting at all.
about diamond doves... they also have different poop... in my opinion its easier to clean up than the quail poop as it comes out in these little donut shaped balls and it dries out faster. the one thing that i found with housing diamond doves with the finches is the finches would pluck them a lot
one of my females was plucked severely, so now i house them separately. this may not be a concern for you as your aviary seems like it is going to be very spacious!! also, diamond doves aren't the best at aiming at where they are going to land, so they do flap around a bit and at times they can spook the finches. but, overall, they are beautiful and very sweet. they have very calming cooing noises and are very dedicated parents