Hi Kenna. My 11 year old has had numerous (three?) sinus surgeries so far. I think. I've lost count. The first one was inpatient and they admitted him for a few days before to get plenty of antibiotics in his system for protection. I was nervous about it and of course stayed with him nonstop, but was pleasantly surprised by the ease to which he took to the packing, which was really minimal compared to what I expected. Frankly, he hadn't understood how to open his mouth when he sneezed, so he blew out a batch of it the first time his nose tickled. He bled somewhat, but it wasn't bad at all and they didn't replace it. He was discharged in just a couple of days, although they had anticipated up to a week.
I will tell you that there are many different methods used to revise the sinuses and your surgery could fall anywhere on the spectrum. Generally though, I found that my little guy wasn't really bothered by mouth breathing, since he had polyps before the surgery that were blocking his sinuses anyway. He was kinda used to an uncomfortable way of breathing already.
The best part of course was his reaction after the surgery and recovery. He noticed how differently things smelled, that he could chew with his mouth closed, and that he felt as though he could breathe so much more deeply. His polyps do tend to grow back yearly or so, and they have tried different techniques to extend the time between surgeries. If you're interested, there was a time I posted a great deal of detail regarding various methods. Just search, and I will try to post a link or two. But he has never been afraid to do another sinus surgery - which speaks volumes. I think you will be very glad you had it done. The first time is the scariest because it's unknown. But you're in good company - sinus surgery is very much standard fare for many many CFers. Good Luck and enjoy your clear sinuses when it's done!