I have no experience with Illinois plans, although the main office I bill for is in Illinois. We don't take any Medicaid/replacement plans. I do bill for offices in PA and FL that take Medicaid replacement plans, so I can tell you what I know about those:
1. Turnaround times on claims are normal, so long as you have made sure to get all referrals/preauth's done before you submit the claims. This is time consuming. Payment is awful, also.
2. You cannot restrict how many patients you see, and in fact, must see them in a certain amount of days from when they call to make an appointment, based on the urgency of the appointment. Each provider manual explains all the time frames. You also can't keep the patient waiting in the office to see the doctor for more than 45 minutes without telling them you are running behind, or the patient can file a grievance.
3. You have to have after hours contacts in place for emergencies, you can't just tell someone to go to the hospital on your voicemail/answering machine.
What I would do if I was you is to go to the websites for any plans you are thinking of joining, and download their provider manuals. You will find all the info you need there, generally. Try looking at Meridian's, for instance. That is an Illinois plan that I pulled up.
Also, some anecdotal advice...for awhile, the specialist office across the hall from my practice was one of the few in our county in Illinois that accepted Medicaid/replacement plans. I am friendly with their office manager, and she told me that they literally had one employee whose entire job it was was to handle the administrative work involving the Medicaid patients and their claims. She did all the auths, referrals, claim submittal, denials, etc. And yes, they were swamped with Medicaid patients. So they withdrew from regular Medicaid, and just stayed with Medicaid replacement plans. It didn't really help, so they withdrew from all Medicaid entirely. It was truly a quantity over quality issue for them. While they of course want to be of service to everyone, it was killing their business to be involved with Medicaid. A lot of the problem was that they were one of the only providers in the area in that specialty who accepted Medicaid. So I would try to investigate how many other providers of your specialty in your area take Medicaid. If you will be the only one, I don't think it will be worth it.
Just my two pennies...