For the most part. If you have medical issues, they won't want you.
You will start competing for a Field Training spot (Enrollment Allocation or EA) on day one. Your EA package gets sent to HQ ROTC around Dec/Jan and you find out in Mar/Apr. So, effectively, you'll only have your first semester to compete for an EA. If you don't get an EA, then your future depends on how your detachment operates. They could invite you back to compete the next year or they can chose to not let you come back. It's subjective and each detachment does things differently.
When you contract, you're agreeing to some sort of commitment. If you graduate and make it through the program, then you commission. If you somehow manage to get dis-enrolled during your last two years of ROTC, they could technically force you to enlist. For the most part, this doesn't happen anymore. If the AF paid for 3-4 years of your schooling then they could ask you to repay or enlist.
In terms of scholarships, you are only eligible BEFORE you contract. You can't get a scholarship as a junior or senior in the program. So for you, you will compete for a scholarship during the Fall semester. If you don't get it, but receive an EA, then you will compete during the Spring. After that, no scholarships.
What you need to do is contact the Unit Admissions Officer (UAO) at your nearest detachment and schedule an appointment with them. Their job is to find suitable cadets who have potential. This forum is a great source of info, but only the UAO knows exactly what is going on. They'll make sure that you'll leave with all your questions answered.