Welcome to PT, happy you are here.

Jen gave you all the good basics. There are other things that can be done, but most of them are if you have problems.

The hissing, growling and even occasional tumble are all normal. There are just getting to know each other and establishing a chain of command, do to speak.

I would let the new kitty settle in and then depending on how you feel about it, some supervised meetings.

There are no hard and fast rules, I only wish there were. It is more of, get an idea of what might happen then see what does.

Let us know how it is going, and please feel free to ask for advice or reassurance if you need it.