The best answer I can give you is "don't".
Honestly, unless you've got really deep pockets and a willingness to beat your head into a wall, Chicago is not necessarily a market where you want to start another franchise.
Minor league football doesn't really exist (except on a semi-pro level), and Chicago already has multiple indoor franchises, so I'm not sure where you'd find a niche.
The ABA has failed multiple times in multiple locations in greater Chicago, so that's a brand you might want to avoid -- not to mention that you get no help from the "league" at all. See the... oh... thousands of posts here and elsewhere about the failure rate of the ABA.
The PBL is already in Chicagoland -- the Muscle play out of Harper College (a fact which, I gather, not a lot of people there were aware of). I'm sure you'd have no problem finding a gym -- the question is, are there any paying customers?
All kidding aside, I'll end with a more-serious joke - the one that goes "How do you make a small fortune in sports ownership? Start with a large fortune." Unless you are prepared to lose a lot of money early on, with no hope of recouping it, don't even open the doors. You'll save yourself a lot of grief.
On the other hand, if you ARE prepared, with sufficient cash reserves... and you realize this is going to be a very expensive hobby... well, good luck!