我学习在大学, bad order, 我在大学学习 sounds better,
In Chinese it's usually subject+place+verb as opposed to European languages with subject+ verb+ place。
苑老师又热情又公正。公正 is too big a word here。 It's more used for a political system or a court。I guess you are trying to say he is fair or he is impartial, in which case I would say 范老师很热情,对学生也很公平。
What you wrote is not wrong though,just the word 公正 is too big for just a teacher。
我觉得她是理想的老师 again not wrong,just the word 理想 sounds a bit funny in this sentence structure. I would say 他是我心中最理想的老师, just sounds better, hard to tell why。
三个课 : 三节课 is better。 节 is a better unit word for 个 for classes。
You have expressed yourself very clearly though, which I think is more important than grammatic details。