Guaranteed spots:
SEC - 3
B1G - 3
BIG12 - 2
ACC - 2
Top G5
ND based on win/loss record and ranking.
The remaining spots can be at large based on ranking IMO.
Then just do the standard brackets. You can even re-seed based on who advances, or just stick to how the bracket is set up. Could still have the first-round games played at the home of the higher seeds.
I don't like giving more guaranteed spots to the SEC/B1G, but I also understand that for this work others will have to continue to make exceptions for them to have more.