Class size is usually pretty small. I'm taking two classes this winter with less than 10 students registered, and my largest class has 17, if I'm remembering correctly. The further you get into your program, the smaller the classes get and the more individual attention you are able to receive.
Transy is great about giving AP/IB credit, and I was able to start out as a sophomore--I'm no graduating early, because of what I chose to study, but I get to register for classes and pick housing before many of my peers, which is great.
The professors are pretty great at what they do, and they all want their students to succeed. They are very understanding of extenuating circumstances, and are typically very easy to get in contact with.
Transy runs on a credit system, not credit/hours. Full-time is considered 3-4.75 credits, which is 3-4 classes, with room to tack on extracurricular music or athletic programs, or less rigorous independent-study courses. This system makes it very easy to manage your workload. For example, I was in four classes, on the academic team, in a sorority, and worked two jobs (one on and one off campus) last semester. And I still had time to have a social life and watch too much Netflix.
Some major programs are more popular than others, such as psych, anthropology, biology, and Spanish. These areas are somewhat hard to register for, but overall, it usually isn't too hard to get into classes you want and need, especially after freshman year. The first couple of semesters, just make sure to have a couple of back-ups in case that GE you wanted filled up. After freshman year, it is also fairly simple to ask a professor for a course-pass, especially if you need the class, and you need it *this* semester to keep on track with your four-year plan.