I've got M60s with a VP180 in my theater which is 14' wide by 24' deep. My ceilings are just shy of 8' and the VP180 is great in that room with the ability to go into even larger spaces. The M60s hold their own, but I can only imagine how M80s would sound.
I have an older SVS 20-39PCi sub that does the LFE dirty work, but I can't wait until I build my own sonic twin to match it and get even more bass. Will it do the job? Absolutely, and it does it well, but multiple subs really sound a lot better than a single sub.
So I think that you are perfectly on track with the M80/VP180 combo and a good sub. Enjoy it now, and add a second sub as finances allow.
2-M60s, VP180, VP150, 4-QS8s, 4-M3s, SVS 20-39PCi, DIY Sub, 8-Shakers, JVC RS45