Ok here is the simplified answers to the clown fish issue
your nemo wether it be a true or false perc can be paired up with a true or false per or a black/white and thats your best options for paring up your nemo. also get one that is smaller than your nemo because if your nemo has been the only clown in the tank for any lenght of time it will be the female even without a male/juvi present
as for the maroons the ones your fish store has that are under an inch can be paired together just get the smallest and largest in the tank or watch for 2 that "hang out" together and as they grow they will size diffrence at the 1" stage they are still unsexed juvis
most likley you will have to set up a seperate tank for nemo if you get a maroon, my juvi pair of maroon clowns will run off a 3" niger trigger a 7" clown trigger, a 7" asfur angel and a 10" sailfin tang in a 215g. . my old lady (5" gold stripped marooon clown) ran a 7 ft 210g tank (rip old lady)