Paradise fish can be quite aggresive little fellas, so be careful what you put them with.
The males can also go hard on the females as well.
Yes, you are correct, they don't need a heater, but a rise in temperature will improve the chance of breeding them.
Not too sure if I'd winter them outside tho, especially where you are, compared with where I am.
They are a bubble nester similar to the betta, so once the spawning is over,
remove the female, Dad will do the work.
Alan 104