I also rode in IHSA
What division you get placed in depends on your previous riding and showing experience. The college I went to had a huge IHSA team, so unless you were a point rider, you didn't get to jump very often (since shows usually limit the number of jumping entries each school can have, we all had to take turns).
Prior to college I didn't show at all (I didn't have a horse and my parents weren't willing to pay for me to show on a school horse), so that placed me in Advanced Walk Trot Canter. It's actually GOOD to be placed as low as you can go - if your coach is on the fence about putting you in WTC or Novice, for example, pick WTC! Then it's that much easier for you to be good ;) I breezed through WTC and wound up regional champion, then I breezed through Novice the next year too with all 1sts and 2nds, then by the time I was a senior I made it to Open. However, since our team was so huge I only got to jump twice a year so it took me all four years to point out of Novice fences.
Some colleges help fund the IHSA team, and others do not. Our team was considered a club sport by my college, so they did not give us any funding. We had to pay our entry fees, as well as fees for the coach, hotel, transportation, etc. It wasn't horrible, as we rented a big bus and put 4 girls to each room. It was SO much fun :)
Based on your description, you'd be put in Walk Trot Canter - you could not be Walk Trot, because that was limited to people who had been riding for 2 years or less (unless they've changed the rules since I was in college)
My school competed against Murray State :)