Hi, nice to meet you guys! I have a bit of a story, here, so please bear with me. ;;

I'm 18, and I work at a wildlife rehabilitation center/sanctuary. About a month or two ago, a woman brought in her BP who she'd had for 10 years, said her son was going to college and couldn't take him. Brought his setup with her, stressed how good he is with children (was apparently used for a children's church program for many of those years). We told her we'd find a home.
This snake has SUCH a good temperament. He's totally chill with being handled, and will literally loop himself around you and relax there. I knew I wanted him, but ultimately didn't want to have to deal with sneaking a snake into a dorm myself when I don't even know what school I'm going to yet! In the end, my coworker's roommate said he would take him.
However, my coworker told me that he hasn't been taken care of properly. She's found his water dish bone dry, his heat lamp off, she's the one who feeds him, etc. They didn't even get a proper fitting lid, plus his tank is being treated like a coffee table. She found his water empty one last time and took ownership of him a couple of days ago. p:
She remembered how much I liked him, and offered to give him to me and take him back when I have to leave for school (she's in her 20s, already earned her degree). Rn I'm mulling it over, because obviously there are quite a few what-ifs in this scenario!

His current setup is pretty decent, although I'd still need to set up a temperature gradient + I know no one's monitored the humidity levels at all. He's a good eater, and has eaten a rat every week since he went home with her. She's already ordered more hides & a proper-fitting lid.

A friend of mine has & breeds snakes, and she already supplied me with this care sheet so I know what needs to be done, for the most part anyway.

Here's my question: If I take this snake, I want to make sure I don't stress him out. Like I said, he has an amazing temperament. The other day I was hanging out with my coworker, and I took him out for hours. I didn't want to put him back because he was very cold, and as I held him he got warmer & more active. What signs should I be looking for, to show that he's had enough out time?
I just let him hang around w/ me while we watched tv. She also has pet rats, so he slithered around and smelled the box they were hiding in. Squeezed himself through a toilet paper roll, which was funny. p: It was hours before he curled up into a ball under my leg, and hissed shortly after (first time I've ever heard him hiss). I put him away immediately, but I know too much handling is bad for a snake and I can't find a straight answer for how long it's ok to keep him out. I've read that there are tell-tale signs like... him trying to get away from me, or hissing, but it took so long for him to get to that point & I'm afraid I'm missing something else.
If I were to keep him, I'd want to handle him a lot (I'd probably chill on my computer with him in the evening after work) but only if it's ok to. ;; I don't want to take responsibility for this snake unless I'm 100% sure that I can take care of him properly!

Sorry this post is really long!!! ;;