If the plan is to operate as one conference then 24 full members doesn't make sense. If you end up with 22-24 full members then you're going to end up operating as two large 11-12 team conferences that just have a playoff at the end of the season (which could mean less postseason berths, which will lead to a split). As of right now, I think the best move is to go to 20 in football by trying to get schools to join for football only.
Temple is the first and most obvious target. San Jose State would be a good addition for football only and they'd easily find a non football home in the Big West. After that, there aren't any established football only options (but UMass and Charlotte will be targets in the future). So two full members are needed. Getting back into Florida is a must so FIU will probably get in. The last school in would be between N Texas, La Tech, and Utah State. Since the Eastern schools got FIU, the Western schools will probably get Utah State in exchange.
Divisions would be:
East- ECU, UAB, Marshall, FIU, Temple*
South - S Miss, Tulsa, Rice, Tulane, UTEP
Mountain - AFA, Col St, UNM, Wyom, Utah St
West - UNR, UNLV, FSU, SJSU*, Hawaii*
From here you can just let things play out. If AFA leaves, UTEP slides into the Mountain and N. Texas or La Tech is brought in. Hopefully the next wave of expansion is a couple years away and Charlotte and UMass can improve and come into the conference. At that point, the conference could try to go to 24 football members, while keeping a reasonable number of full members.
Ultimately I see:
East - UAB, Marshall, FIU, Temple*, UMass*, Charlotte*
South - S Miss, Tulsa, Rice, Tulane, La Tech, N Texas (UTSA fills in if S. Miss or Tulsa goes to Big East)
Mountain - CSU, UNM, Wyom, Utah St, UTEP, NMSU
West - UNR, UNLV, FSU, SJSU*, Hawaii*, Idaho*
BYU is preferred over Idaho but I don't think they'll go for it. 18/24 keeps the conference at a reasonable size for non football, and will still allow them to have their semifinals in football. There are an even number of Eastern and Western schools so divisions are simple. You go bigger than 18 or 19 full members and this conference would last.
Due to various NCAA membership rules currently in place, I would think if the number were 20, you'd have to have (2) 10 school divisions, ideal for 9 game conference schedule. You then can do a "top 2" in each division for the "semi final" they are proposing, which would fall within the current rule structure. Winners of the "top 2" divisional games goto the final.
Now for 24 schools, I think you could have what would be (2) "pods" per division (since we're so used to using "League" for the mother entity, "conference" for the 2 separations, and "division" for the splits within a "conference"..."pod" is the word we use now since "conference" is the mother entity). The "divisions" would need to remain the same each year, with the pods remaining the same. In accordance with the NCAA rules, the championship game would still be the winners of the (2) division league. Can still do 6 and 6 "pods" for each division with those 2 winners playing each other, winner to the championship game.
In theory, the same could be done for 20 schools with 5-school pods, and divisions of 10...just that it wouldn't be 1 vs 2 in the semifinal, it would be PodA #1 vs PodB#1.
The easy move seems to be to just bring in Temple for FB only, to help out with ECU and Marshall, and add some northeast TV to the Countrywide Conference. I do think there would be some benefit if there were more schools, if we talking solely from a market angle (for TV rights gains):
North Texas: no Dallas schools in the conference now, UNT fills that void.
Utah St: replaces lost SLC market, keeps conference relevant in Utah where so many nearby schools exist.
SJSU: program hasn't really done much, but it's the Bay Area, and there are a ton of TVs there. A local school would help turn some of those games on peoples TVs.
FIU: with no Florida presence, and none of the Top 4 options available, FIU makes some sense. Like with SJSU, it's some access to the Miami market in a day when networks are paying big money for live sports rights. FIU games might actually do better on TV if the market is getting a nice variety of schools from around the entire US...albeit Temple (Philly...snowbirds retired in Miami), ECU, UNLV, etc.
UMass: new to FBS, haven't done a thing. But if you add Temple, you do push the footprint north to the population dense region. Adding a western MA school playing in the Boston market would help. Living in Boston, with so many UMass alumni, I can tell you that a UMass vs UNLV game on TV would get more eyeballs than Umass vs Akron. Now, a UMass vs ECU game, that might get more eyeballs than BC vs Wake Forest.
Countrywide Conference (20 schools):
East Pod: UAB, Marshall, FIU, Temple, UMass
South Pod: USM, Tulsa, Rice, Tulane, N Texas
Mountain Pod: CSU, UNM, Wyom, Utah St, UTEP
Pacific Pod: UNR, UNLV, FSU, SJSU, Hawaii*
Lots of other schools that might make more sense over Temple, Umass, etc. Schools like LA Tech, Charlotte, App St., GSU, Georgia St., etc. It's just a matter of the conference doing what is best for their TV deal. To humans, adding LA Tech, North Texas, Utah St. would be a gimme. But when factoring in TV for a coast to coast conference, schools that shouldn't be in the discussion actually are.