Compatibility in freshwater aquarium

Question
Hi,

I'm almost done cycling my new 20g and have two fish left that survived the process (long ugly story now resolved).  Anyway I've got a platy and a molly (whom I THINK are both male - I've found drawings and I know what to look for but bc of the cycling stress they're still keeping their ventral fins clamped a lot of the time).  I won't add any more fish until I know it's done cycling (zero ammonia and nitrite, some nitrate, clear water) but then I want to add a fish or two at a time until it's stocked.  My question comes from researching compatibility of different species on the internet - it seems so confusing as they all say something different!  What I'd like to eventually end up with is:

- one more molly and one more platy (try to get females as I read males will harass each other, and no more as they'll likely breed)
- eventually a betta
- four to six schooling fish

Question: if I end up with two male mollies/platies, will they hurt each other?  and if I have males and females will the tank soon be overrun with fry?  Options for the 'schooling fish' I'm considering are bloodfin tetras, diamond tetras or zebra danios - is one of those preferable for the betta?  what about rosy barbs? and what order do I add all these in, as I've read you shouldn't add one to three tetras bc they'll get stressed?

20g tank, lots of plastic plants all different heights and lots of free space too, bogwood, rocks, power filter, airstone, added salt and Cycle, temp 78 F, pH neutral, currently zero ammonia, 0.5 ppm nitrite and 5 ppm nitrate (still waiting to finish cycling)

Appreciate the help...

Answer
A male betta won't go with any of those fish, however I female betta could work, but you would have to get zebra danios as the schooling fish.

If you have males and females the tank will be overrun with fru, unless you don't have many hiding places, then they will all be eaten. Danios are very effiecient at this.

The males don't really fish each other. They bother each other, but its nothing to worry about.