I bread Tetras fish for 4 of my LFS. I have 5 55 gallon tanks using a 75 gallon sump for my fish that I will bread. I use 20 longs for the breading. I move them to 55 gallon grow out tanks (20 of them) that has a 100 gallon sump. All my sumps do use UV on a portion of the water going through the sumps. For the final Q tanks I use 20 highs that use sponge filters and the owners come and get them on Fridays, they buy the fish by the tank. I don’t make but about $500 a month by the time I pay the power bill (I have well water) and get new stuff.
I would go with canisters on the large tanks and sponges on the smaller tanks. I think that heating the room is the best but can be hard to keep a room from 78 to 80.* I guess you’re not looking at about 10 to 15 tanks to start with so heating each tank will be the best. I would try to find a large water holding tank around ½ as much water you are planning to use in a week. This way you can “air off” your water. Most of the time this will stop the use of some chemicals be added to your water.
Good luck with your Guppies and remember you will have top do something with all that aren’t up to your likeing and I guess send them to your LFS. I would get to be good friends with them.
I don’t count any of these tanks as my pet fish, but there part of my living now and with all the tanks I have it’s going to be too hard to stop.