Welcome to BYC!
Please do tell us where, in general, you're located. Climate matters, especially when it comes to housing and it sounds like you're in an area where heat is going to be the problem.
Here's an article for you:
https://www.backyardchickens.com/articles/hot-climate-chicken-housing-and-care.77263/
You're going to want BIG ventilation -- something no prefab coop has -- and that will render insulation moot anyway. In fact, depending on just how hot your summers get, you might be needing to think about an Open Air coop rather than an insulated one.
BTW, you absolutely cannot trust the numbers prefab coop manufacturers claim about how many birds their coops house. This is what you want to look for:
For each adult, standard-sized hen you need:
- 4 square feet in the coop (.37 square meters)
- 10 square feet in the run (.93 square meters),
- 1 linear foot of roost (.3 meters),
- 1/4 of a nest box,
- And 1 square foot (.09 square meters) of permanent, 24/7/365 ventilation, preferably located over the birds' heads when they're sitting on the roost.