Needs more than just 18 teams.

IMO, you go with an easily divisible number like:
24, 32, 48, 60, 64, or 72

Personally, I would do 6 conferences with 12 teams each (72).

The 6 conference champs make the playoff.

Top 2 teams in the polls get a first a round bye.

Conferences would attempt to be both regional and maintain traditional rivalries. Each conference would play only 8 conference games, and each team would be permitted to have an optional permanent OOC rival and cross-division rival.

The 72 teams that I would pick would be basically the P5 plus a few extra teams here and there. The conferences would largely resemble the status quo before the Big 12 blew up, but with some noticeable differences here and there.

All tv revenue would be shared equally by all teams and all conferences, but conferences negotiate their own deals.

Pacific
North
Washington
Wazzou
Oregon
Oregon St
BYU
Utah
South
Stanford
Cal
USC
UCLA
Arizona
Ariz St

Big 12
North
Colorado
Iowa St
Nebraska
Kansas
Kansas St
Mizzou
South
Texas
Texas A&M
Oklahoma
Ok St
Baylor
Texas Tech

Southeastern
East
Florida
Georgia
South Carolina
Vanderbilt
Tennessee
Kentucky
West
LSU
Arkansas
Ole Miss
Miss St
Alabama
Auburn

Atlantic

North
Boston College
Maryland
Virginia
Virginia Tech
Wake Forest
Miami
South
Clemson
North Carolina
Duke
NC St
Georgia Tech
Florida St

Big East
North
Connecticut
Syracuse
Pitt
West Virginia
Cincinnati
Louisville
South
Memphis
ECU
USF
UCF
TCU
Tulane

Great Lakes
West
Iowa
Minnesota
Wisconsin
Michigan St
Illinois
Northwestern
East
Michigan
Indiana
Purdue
Notre Dame
Ohio St
Penn St