External pumps - Eheim or Ocean Runner are the ones that I would use. They are up there with the most efficient and quietest pumps you can get.
Heating - Use several large heaters in the sump system. for this I suggest the 1000w Jagers. They are the most efficient and will be the most cost effective in the long run. I would look at having a few of them both for efficiency sake, and safety sake (if one goes you still have enough to heat the whole setup)
Overflow protection - Most people use a comb across the top of their overflow boxes. This works a treat for 99% of applications. However, for breeding it is useless. In fact I would not be going with overflow boxes at all. I would be going with drilled holes at the back with sponges covering the inlet. That way the angel fry and bristlenose fry will be fine.
Just out of interest, how do you plan to filter all of this? It will have to be one big-arse filter! Most people will generally do 3 or at most 4 60gal tanks on one filter setup. With 6 tanks your filter will have to filter at a minimum 1400 gallons every hour. However, if you are like me and like to aim for more that filtering the water in the tank 4 times every hour, you will need more. I like to aim for at least 8 in grow out/breeding tanks which is 2800gallons every hour (over 10500litres per hour for all us logical metric people
Thats a LOT of filtering. I'm thinking multiple trickle filters leading into a central sump system...oh man, you are going to have SO much fun building this! If i was a rich man I would love to take the time off and help. Epic Project!