I think if you do 8, you give 5 automatic bids to the Power 5 champs, and you can make a rule that says something like "the top ranked Group of 5 team gets an automatic bid if they are ranked in the top 8" or something. That way you get 2 or 3 at-large bids for the committee to award, and then they seed the teams and set the matchups.
That would have given us Alabama, Clemson, Ohio State, Oklahoma, and Washington as automatics, and presumably Notre Dame, Georgia, and Central Florida as your playoff teams this season. If we seed them by the way that the committee ranked them, we would have the following bracket.
1)Alabama
8)Washington
\
Winners
/ \
4)Oklahoma \
5)Georgia \
Championship
3)Notre Dame /
6)Ohio State /
\ /
Winners
/
2)Clemson
7)Central Florida
Play the first round games at the higher seeded teams home field. Once it's down to 4, play it out like the current format, with the various major bowl games rotating locations. That's gold.