Before the point on the schedule itself, the league configuration must be determined. It may be better asked in the main forum to help find out for sure, but I think your 2 sub-league idea would actually be the situation where playoffs would not be possible.
I know way back when in OOTP6 having a different number of divisions in the subleagues (like 1 division in one and 2 divisions in the other) would not work, and I believe that still holds true. However, since after OOTP6 I think that single-league playoffs are fine meaning you could do the single sub-league with 12 teams. If my thinking is correct you could have 3 divisions in it with a wild card making 4 playoff teams or just one division with the winner and either 1 or 3 wild cards.
Hopefully someone here or in the main forum will confirm that. I have not played a lot lately, so I have lost track of how all this exactly does/can work.
After the configuration is set the schedule can be composed. On first glance I am not sure how the 30/8 could be broken down best. I will give it some thought.