If you really want to do it by the book, you should aim for room temperature of approximately 65 to 75 degrees Fahrenheit, no matter if it's haired or skinnie. Whatever you do when it comes to cage location, make sure to keep it away from direct sun or heat sources. I'll leave you with some...

To be sure, always wash your hands right before you play with the little ones or feed them. And if you need to cough, take your distance before you do it too. There's no proof that our animals can actually be affected, just a few isolated cases in dogs and cats, apparently. But you never know...

I know I made an unorthodox decision, but when my guinea was small, I used the old cage my hamsters sat in (https://popular.reviews/hamster-cage/), only after he grew I switched to a bigger specialized cage (and obviously got a new hamster to fill the vacant one, love these furry creatures).

I've seen rats and guineas in the same room before at a childhood friend's house. There was no interaction, obviously, and they didn't seem agitated or nervous at all, so there's no reason to worry about the schematics of it all.

They love tunnels, make sure each has their own too. Other play stuff that will probably delight them are woven grass play balls, small hammocks (yes, these exist), and chewing hanging toys.

If the area is large enough and you keep an eye on them to make sure they don't become aggressive with one another, things should work out just fine. In my experience, the piggies are usually quite sociable and friendly. :o

It's a boy. But when you do take the small one for a vet check-up, you can ask there too just to be sure.

It's all fine, what's important is for him to eat as much hay as possible. I have a guinea and a rabbit, both are on a similar diet, and have never had issues with their weight or health. But they do indulge in hay a lot.