Corys like to be in groups, and the betta will most likely attack the platies if it is male. You could do:
4- Albino cory
1- female betta
2 platies
Or you could always do like 4 female betta and 3 or 4 corys. Just a thought as I personally do not like platies. Maybe instead of them you could do some guppies. Up to you.