To touch on OP's original question on when you should be betting futures, it's a good point that if you have a small bankroll you don't want your money being tied up. I think King Yao had a section in his book where he talks about what you could have been making during the same time period. So for example, if your roll was $1000 and you put everything on a win total with 5% equity, you shouldn't do that if you can make more than 5% on that $1000 over the period that the book holds your money. This makes complete sense if you use that example.
Maybe I'm not smart enough to understand this but I don't see how it applies when it's not a significant part of your roll. If I'm betting 1% of my roll on a future, and I'm not decreasing my bet size (even though it's now 1% smaller), I don't see how it's an apples to apples comparison.
Letting the books hold your money sucks, but you need to also think of it as an investment. If your equity in a future is 5%, and the football season is 4 months, you're not getting 5% in any other kind of investment over 4 months.