Just my opinion garner through a decade of breeding colubrids: I don't want to start any fights. 
Bring the new female up with the rest, she'll be ready.
Some of these guys might disagree, but I keep my snakes in the fifties throughout brumation. Temps in the 70's will likely cause significant weight loss.
Remember your pyros are cool weather critters, they function normally at lower temps than your average snake, I would keep them in the 50's as well.
AGAIN MY OPINION, but I would use something a bit more organic for a laying media. I prefer spagnam moss, or vermiculite to that styrofoam stuff, yuck.
Here's my method, keep in mind I use plastic blanket tubs and not aquaria.
When the female is heavily gravid and close to laying, (usually about two months after mating) fill the cool half of your snake tub with moist spagnam moss. (the half away from the heat tape.) Leave the hot half covered in newspaper or whatever dry media you were using before. Remove the water bowl if it is large enough for the female to get inside of, and replace with a wee one. (to prevent her laying in the water.) At the same time you make these preperations, set up and calibrate the temps on your hovabator. Make sure its ready BEFORE she lays. AND prepare the containers in which you intend to incubate the eggs. Have them set up and waiting for their arrival. This way, they are at the appropriate temp and humidity when your future babies arrive.
Here's my method for incubation tub set up. FIRST choose a container that is a bit larger than you think you'll need for the ammount of eggs you will be getting. Make sure there are holes punched in the sides of the container to allow air flow. Eggs can suffocate and or drown! The more media you have, the less likely it is to dry up during incubation. I use vermiculite because it is easier to tell when it dries out, but perlite is fine.
To prepare the incubation media: Mix a bunch of vermiculite and water together. Reach in and grab a handfull of vermiculite and squeeze it until no more water comes out. It should stick together like a snowball. Put the snowball of vermiculite into the incubation tub and repeat until full. Obviously, leave room for the eggs and the babies. Put the container in the incubater so that it is ready for the eggs when they come.
LAYING:
She will root around in the moss you put in her cage, and make a little indention. When she's close to laying check her twice a day so you don't leave the eggs too long. If you're lucky, you'll get to watch her lay them. Once they are laid remove them from her cage. BE CAREFUL not to turn them from the position you found them. You can mark them with a pencil to show which end is up, but that is usually not necessary. Place them in the incubator in the warm, ready tubs you have already prepared. DONE! Now wait a long boring two months and you should be rewarded. 
As far as filling the bottom of the hovabator with water, I've never found it necessary, but I live in a rather moist climate, if you find your media is drying out a lot dump some water in there.
And on the subject of a hatchling rack, I like your creativity, but don't half-ass this step. Shoddy cages lead to escaped/dead babies. You don't want that. When they first hatch, and really for however long necessary, you can house them all in an adult size cage with smaller holes. I've not heard of many instances of siblicide in alterna. Have fun. and good luck getting them to eat. 
dAN
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