I know they should be fine with the danios, platies, and mystery snail, and I think the
Dwarf Gourami.. Should be fine but im not sure if gouramis/danios and livebearers (too late you already got platies so ya) need different water parameters.
Depending on the male you could get a male and a female if you want. Some males are much more... pushy... sexually than others... so if you get a male and female, if you end up with the male constantly harassing the female then you might need another female...
You could also get 2 females. They'll likely be pregnant from the fish store and will give birth to several drops of fry before they run out of stored sperm.
Or you could just get 2 males. Males often have longer more pretty fins, and since your not looking to raise the fry you could go this route.