1. Same deal as Sourire.
2. I'm currently going for a Ph.D. in astronomy; my main interests lie in planets and instrumentation, though my current research isn't anywhere close to those.
3. The idea to study physics/astronomy in particular came to me in high school, but it was an evolving process. I knew from an early age that I would go into a technical field of some kind; initially I thought I'd follow my parents footsteps and become a programmer of some kind.
4. Because it was interesting, cool, and I had/have an aptitude for it.
5. Nope. I decided early on that I wasn't going to take on that kind of workload, since it didn't really fit in with my goals anyway.
6. No, unfortunately. However, I did get to do research, but I had to go looking/asking for the opportunity, and I never did get paid very much. Now, being a grad student, I get paid for it, of course.
7. The most difficult part of physics? For me, I never did get most of my second quarter QM (I think my good understanding stopped after perturbation theory and some basic radiation stuff). Stat mech sucked big time, too. In general, though, it was mostly the problem of how to get from A to B using the information given - the goals were always clear, and even what I had to do was usually clear, but actually doing it, and understanding what you were doing, could get pretty difficult. For instance, I never did get very good at setting up those geometric integrals in EM.
8. Yeah, I'd say so. I knew going in it would be hard, some subjects would be harder than others, all that. Despite all the work, it was a fun ride, and I made some great friends along the way, professors and fellow students alike. Research was/is a blast.
9. I'll almost certainly be a published author in a few months. That'll be something to be proud of. For my undergrad career, probably knowing I helped put together a working astronomical instrument prototype (well, before we rediscovered the aluminization chamber...), and pulling a couple of people through the program who might otherwise not have made it.
10. Recognize that it will be hard. Sometimes almost soul-crushingly hard. Don't give up. If you're struggling or stuck, ask for help, and do it early. Get to know your fellow students, and do the homeworks together with them. Go to your professor's office hours, and come prepared with questions so you can use the time wisely. You'll probably pull through and even get a better grade than you were expecting.