Hello,
I think it is not necessary to separate one pair but it is helpful to control them and to have more juvenil.
The light is not so important, they feel safer in low lighted tanks but swimming plants can help there. (Yes i had seen some really higlighted tanks but I wouldn´t use that for breeding)
Your question about the temperature is not so unique to answer. I think it´s a bit different from fish to fish but in the summer I got 30°C for a short time and none of my fish died.
I hope I can help you!
Bennie