Is this a bad idea for my 40 gal community tank?

I have guppies, 3 panda platties, cherry barbs albino cherry barbs, some tetras and 1 male flaming dwarf gourAmi. What is a better choice, another male dwarf gourami or 2 females? Explain for both plz. Also i would like to add that people say not to put to males together but if that's the case then y do the stores do it? Explain on that to. Also, why won't my albino and regular cherry barbs mate? I have 2 male cherry barbs and 2 females and I have 2 male albino cherry barbs and 2 female albino cherry barbs. One of my albinos is super fat( I bought her like that) and they aren't mating