If they are smart, then they would start the league much like the old AFL did in the 60s. Use castoffs and older named players who aren't going to make much in the NFL or would be just backups. Guys like Brad Johnson who would take the same money we are paying him but be a starter in that league.
The other thing that made them successful was drafting the same guys that the NFL did. Think about drafting guys like Steve Smith in their 1st round instead of the NFL second round or even a third or fourth round guy moving up a couple of rounds. Their cap could (and should) be the same so you know guys that the NFL didn't draft until late second or third getting picked in their first would most likely sign with the new league.
The trick for any business is to give the same impression as the competitor and not overpay for the big names like Peyton or LT or even a Tony Romo. Build stars of your own through the draft.
The next thing is to put teams where they ain't. San Antonio, Las Vegas, Los Angeles, Mexico City, Birmingham, Portland, Salt Lake City, Hartford, Albuquerque, Norfolk, Springfield, Syracuse, Orlando, etc.; places where you could get a stadium that seats somewhere between 30000 and 50000 so that you have a chance to fill it. All of those places love football.
The problem with the USFL, XFL and some of the rest was going head to head with the big name guys or trying the spring thing. But it could work if they say play all Sunday night games or Sunday night and Saturday night during the fall.
Cuban is a extremely smart business guy and knows how to make things work so it will not surprise me to see it successful with him as an owner.