Congrats on starting dental school!
1) After exams. Our school would have a single, large 4-5 hour exam every 10 weeks, so the week after that was always a bunch of parties. Some were private, some were sponsored by the school. Great time to socialize and hang out. I am not sure if other schools do this, so I can only speak for my school. Other than that, I am hanging out with my classmates all the time in the second half of third year and it looks like what will be most of fourth year.
2) Networking advice? Just be friendly with everyone you meet and get to know. Simple as that. This is not big business where your success is who you know. This is private practice where being good to your patients and being professional to your peers is most important (in my eyes).
3) Find an outlet. Mine is photography. I find a creative outlet by going out and taking pictures, editing them, and sharing them. It works since I can pick it up and drop it when needed, so its flexible enough to work for me. Some of my classmates workout, some drink (honestly), some socialize, etc. The key is to find an outlet, because if you don't you will burn out. As far as coping, that is a personal attribute that will vary from person to person. My class is very small at 35 students, so everyone knows everything about everyone here, for good or for bad. As far as working with patients - learn to develop a backbone and thick skin. Know that you will have to jump through hoops in dental school and learn to recognize those loops that way you can do them without raising a fuss haha.
4) I slept probably 7-7.5 hours a night to be honest. There was never a time that I needed to lose sleep so long as I stuck to my study plan. Many of my classmates that took more time off early had to cram more later and got much less sleep. I never felt the need to give up on my sleep in order to study. The key is to be disciplined in your study habits. With commuting, this might prove to be more difficult, but I also have classmates who drive about 45min each way every day and they did just fine.