An ABN will easily take care of 20-30 gallons worth of cleaning as a big juvenile or an adult. With the amount of waste they excrete, more doesn't really mean cleaner. You may not have much algae or leftover food but you will have a lot of poo... That is a big tank but unless you don't mind vacuuming often, I'd go with up to 6, not more. They have a fairly high bioload each.
An average spawn will have more males than females. If you are buying them young and unsexed, it's extremely likely you will end up with more males than females. If they grow up together in a large tank there shouldn't be much fighting. With only several to start, you can always add females later.
With 10 unsexed fish you could easily end up with 6 or 7 males. Rarely does their fights result in real harm but it *can*. I have had one male who killed other males given a chance (he had to leave). At the least, their squabbles can involve a lot of thrashing about which can make a mess of delicate plantings. Females can squabble too but it's brief and less disruptive. They are a great fish IMO, but not one to overstock with.