I agree with the others that you have a good plan. Here At my house the Feliway Plug-ins and spray have helped a lot with keeping every one calmed.

Since you have two cats already then you have good chances of it going well because they are used to other cats. My poor Ripely was an only cat for over 10 years before I introduced more cats to him. It was rough sailing for a while and he still doesn't get along with Scout but it's a liveable situation.

As for spraying, yes neutered males can spray, Ripley is proof of that but it doesn't mean it will happen with any of your guys.

Good luck and I look forward to seeing pictures.