I think you are right, slow is not going to be a bad thing... he will let you know if it is too slow but I think better to err on that side than rush things.
Disregard the hissing at you when you go to pick him up in those situations, it is simply because he feels anxious and stressed about the new environment and other animals...and sometimes that redirects onto whatever is closest (you)... but when he is in his room work on establishing that bond, find treats he likes or certain play he likes and use that to enhance your relationship with him
I find that if you sleep with the new cat for the first week or so, it speeds up the bonding process.