1. There are a bunch around the park, but can't say how expensive it is compared to cheap rates.
2. There are public transit options, particularly in the summer. YRT (York Regional Transit), TTC (Toronto Transit Commission), and the GO (Government of Ontario) all serve a make=shift transit loop at the park.
3. Use this searchable calendar to see how busy the park is on any given date. Of course it can't predict the future but it gives you a good idea of how busy the park has been in the past on whatever days you're considering. (https://queue-times.com/parks/58/calendar/2019/12) If you're there on a day it's open 10-10 and you arrive before 10am so you can start working the busy rides right away before lines build you can fit everything in a day. Definitely takes some strategizing, though.
4. Lots. Blue Jays, Ripley's Aquarium, CN Tower, Hockey Hall of Fame, Legoland (right across from Wonderland), and more.