Welcome to FishLore

I'm sorry to hear about your betta.
What kind of pleco do you have? Most species get too big for your size tank.
Without knowing what kind, I'd say no to anymore fish. Plecos are big waste producers.
Even though it looks like you have room for more fish, you have to take into consideration how much waste they create not just the size of the fish.
I don't breed fish, however, it depends on what type of fish you want to breed.
The ADF's if male and female will breed with no coaxing or conditioning. Guppies and mollies are quick breeders. Others you have to condition them or provide the correct environment for them. And of course, you'd need males and females.

Usually, you'd need a breeders box or net for the fry/eggs or they'll get eaten by their parents.
Then you'd need a grow out tank until they get bigger.
Good luck! Post some pics when you get a chance
