new adult cat

Hey guys, I just adopted my friend's 8 year old neutered tom. She needed to rehome him as he had been her daughter's cat, who moved out this year, and she got a very small dog who the cat kept attacking. I've had him since Sunday and things are going fine. My cat is adapting to him (she is a lone cat but she previously shared with two toms in another house, so she's pretty quick to adapt. He also had a few new siblings during his life, and he seems more indifferent to my cat's whinging and b*tching! He's very easy-going). The cat was an outdoor cat so he's getting used to being kept indoors. Once he's fully used to his new home he'll be allowed in and out as pleases, like my own cat. He used to be sneaked indoors by my friend's daughter so he really feels spoilt rotten at the moment wondering why he's allowed stay in! That used to be his treat! He has started meowing at the window and I can tell he's starting to get cabin fever. My cat has a whole box of toys that just never interested her so I'm giving them to him (keeping her own favourite toys away, so she can still have those) and he seems to love them, he never had toys before. I live in a shared house but I have my own sitting room, so I am keeping new cat in there all the time, and still bringing little cat up to my room to sleep, as she always did, that will always be her safe place. Big old tom here is the friendliest cat, he didn't care in the least about moving in with a new person! He's super affectionate even though he barely knows me!

Things are going very well but I was just wondering if anyone has any advice about how to make his next couple of weeks more interesting for him I suppose! I can't let him out obviously. I have also heard very conflicting advice about how long a cat needs to stay in before they can be allowed out. Given that this guy lived his whole life about a 20 minute walk on human legs from here, I'll be keeping him in longer than I did with my cat when we first moved here. She escaped after 3 days and just stayed round. I know that was just lucky! I'll be gauging the situation. Any advice I'd love to hear. I do need to microchip him before I let him outside. It might be stressful to bring him to the vet and back again too soon after his move? I think they're both very clever cats (and that's not bias, I've had a lot of cats and this pair aren't thick). Thankfully also my little cat is very attached and affectionate to my landlord and getting to know the other tenant now, so she's always got other rooms to go into. She normally watches TV with my landlord all night then only comes back to me when his fire burns out and it's getting cold!

Oh yeah, meant to add, Amelia, my little cat, is used to eating in the hall so I feed her out there, but she still does come in and eat the food in the sitting room too, which is promising. She's almost allowed to eat as much as she wants. New cat is obese and thankfully I have Amelia on the sterilised food anyway (to allow her to eat what she wants without her getting fat) but he is obsessed! Even when he's upset and stressed if he sees food he forgets being stressed, eats everything he can see, then remembers that he's stressed. So feeding is actually the least complicated thing! I give Amelia her total allowance in her bowl in the hallway in the morning, and she will snack on that during the day. I give Corey tiny bits during the day, because he will gorge himself and then keep wailing for more.