First off, welcome!
While I am not sure about having the side "surrounds" in front of the listening area, or that you will gain much with a 7.1 vs 5.1 setup for a space relatively only 16 feet deep, I think that you are off to a good start and the basement will be a great place to entertain.
Did you already purchase the Yamaha in ceiling speakers? With direct radiating speakers like that, mounted above and in the case of the "side surrounds," in front of the listening area, I think that the surround effects in movies will not be what you would hope for. After all, in 5.1 and 7.1 setups, the layout is designed by the mixing studios to have speakers pointed from the sides/back of the listening area, not overhead. If you already have them and can't return them, then you might do better to have a pair mounted in the wall to the rear of the seating area instead of the ceiling. Then mount the two "overhead" ones shown in front of the listening space, more off to the sides and back at least in line with the main viewing seats. That would help to give the sense of a real surround installation using in-ceiling speakers than just mounting overhead.
Again, I think that you are off to a great start by just having a plan of action. I will see if I can dig up a speaker location document. I know that there is an article here about it.
Welcome again and please take my comments as just someone excited to try to help.
M60s,VP180,VP150,QS8s,20-39PCi,DMP-BDT210,HD-A2,JVC RS45, Onkyo TX-NR709, Shakers