As someone who just went through this, let me to tell you to be prepared for some stress for a little while.
They have to work out the whole territoriality thing.
I adopted a 3 year-old f cat in Dec and then a 2 1/2 year old m in August. It's been a month and a half and things are relatively calm now. They're not best friends yet (although the m would like to be) but they get along OK.
I suspect my f really likes him more than she lets on but won't give him the satisfaction. She likes to sit high on the cat tree and watch him play below.
They will sit together for "treat time" and even play with opposite ends of a long ribbon if I play with them. I'm very hopeful at this point.
Good luck to you.