Hi Scott, welcome.
I think you've got a good plan!
I've had good luck with Onkyo refurbs and think they are quite a good value. In a small room like that, I think the 508 would be a clever choice.
If you can afford the M22's, they are probably going to give you greater long term flexibility and satisfaction.
Lots of people recommend a vertical center channel (like a single M2) if you like that sort of look and can position it well. Personally, I have a VP100 in a very large room and I think it is wonderful. So, you're probably going to get recommendations for either 3 M2's across the front, or a pair of M22's and an M2 center. You can't really go wrong either way.
Everybody likes Hsu subwoofers
Have fun!
