3 Male Red Dwarf Gourami's In 75 Litre Tank

[FoxesForever]

Hi,

This is my first post see bear with me

I have recently started to keep tropical fish;

I matured my tank without fish, all water tests confirmed all was ok after about 6 weeks

Initially i started with 6 zebra danios, then after a week and another water test to check nitrate amonia etc etc levels
i added 3 red dwarf gourami's (i believe they are all male - orange tail, silver head and blue fins at top) and 1 catfish

my aquarist didnt advise me not to put these 3 males together ??

My question is firstly, is it ok to keep 3 male gourami's in my 75 litre tank (23 inches tank length)

Secondly i have come across conflicting answers on how many fish i can keep in this tank ??

Is it about 20ish adult fish that = my 23inch tank or another equation ?? - please advise.

Also what other fish would be good to introduce into my tank in the coming weeks ?

Thanks
Mark