@ASP -- lots of things I would do differently but my ideas are mine alone. None of these ideas may be your cup of tea so just showing what we did in the past 13+ yrs of chickeneering.
Your temps seem awfully high. At those temps I never put half grown birds outside. Matter is, we kept most of our chicks and juveniles indoors till they were 4-5 months or older no matter what weather we had. Was it a mess to keep them indoors! You bet it was -- with a lot of floor scrubbing in the kitchen (we aren't built with an adjoining laundry room or enclosed porch to accommodate muddy boots, dog crates, or brooders for pets, so kitchen was it).
Here's some pics of keeping chicks or juveniles indoors. The dog crate was used in the den for required one-month quarantine for any new birds before integrating into the backyard. New young birds were house birds till they were old enough and weather permitted to give them occasional supervised outdoor time.
Rabbit fencing with overhead bird netting to give a juvenile limited supervised outdoor time.
Once with only one juvenile to be integrated we made a chicken diaper but it was more trouble to clean up than it was just quickly picking up poop from the tile floor!
It was easier to just let the bird "free-range" the kitchen.
4'x4' dog crate with bird netting on top to keep juveniles from flying out -- we had room in the small den to fit this crate -- used for quarantine
Another time we had several chicks we used a kiddie pool with bird netting on top -- in the kitchen again. Our outdoor temps were 100+ and indoors 90+ so we never needed a heat lamp for the chicks. But in a couple weeks they were too big for the pool and they just used it to sleep at night. They jumped back in the pool & put themselves away at dusk.
These 3 juveniles stayed indoors till 4 mos old because our summer heatwave was brutal that year.
Our most recent cheap brooder set-up this year in the den. These chicks stayed in the kitchen as juveniles for almost 5 months before integrating with the 3 outdoor adult birds.
It rained so much this year we kept them indoors & couldn't integrate the new Silkies for nearly 6 months or they'd get soaked and chilled to the bone.
As for security we learned the hard way that a smaller coop, chicken wire run, and flimsy yard gates were not predator proof. With our first coop two large stray dogs broke into the yard and tried to tear the chicken wire walls to get at our birds -- TG our neighbor chased them off so no birds were harmed but that chicken wire could've been torn to shreds. The coop frame was sturdy but it should've had stapled-down hardware cloth walls and NOT chicken wire. The coop was mounted on paver stones all around so no predator could dig under to get to the birds but the chicken wire was a flaw. And no amount of tarps or pop-up canopies overhead kept the little coop cool in summer or dry during storms!
We quickly found that keeping a couple bantam chickens in a 4'x6' coop/run was too small even for 2 bantams and we had to release the chickens in the yard to roam, forage, sun or dust-bathe, forage, run, flap their wings and do all their natural chicken stuff. We set up a pop-op canopy for shade.
When we remodeled the backyard we tore down the old chainlink fence & tarps to put up a block wall with additional privacy fencing on top and iron bar gates to keep out stray dogs. We divided the yard half for raised garden beds and a people patio and other half as a chicken yard with 3 popup canopies, citrus trees, and dog houses for shade and for hiding. We also removed the first chicken wire coop and put a bigger sturdier dog kennel wire coop/run in its place with its own patio roof to protect from hot sun or rain storms.
As for getting new chicks we get them Marecks vaccinated only -- I don't hatch my own eggs that way we don't get unwanted roo's. We don't feed medicated chick feed but use chick probiotics in their water. We watch that their poop is not bloody and that no chick gets pasty-butt.
And we have a refrigerated arsenal of chicken meds on hand and cabinet-stored first aid supplies. There are BYC threads on the recommended supplies/meds to keep on hand.
It took us over a decade a bit at a time to get our yard chicken-proof and safe. But even with all the sturdy block wall, privacy fencing, and locked iron bar gates, a mountain coyote walked the neighborhood roofs and fences and got into our yard at 5 a.m. TG our coop was sturdy locked! DH called animal control and they captured the critter. City raccoons, possums and feral cats prowl the neighborhood at night so we're glad the barn coop and run are heavy duty dog kennel wire and bolt-locked.
Another predator we have are Cooper's hawk
(chicken hawk) so we cut down aerial flying space with patio roofs, popup canopies, trees, dog houses and benches for hiding.
Enjoy your chicker-doodles and great that you want the best safest environment for them
I could use an extension lead and put their hear plate out too, if that's safe. I'll attach some pics of their current brooder box inside which they regularly escape from!! And some of the outside run set up. 
these pictures relate to the above post 
so far they seem fine. I hope I haven't done the wrong thing and they keep strong and well
