Occasionally they throw in random tschotckies as part of your registration. Once or twice I've gotten shoe laces, and several years got buttons in the same vein as the "Happy Birthday" and "I'm Celebrating" buttons. But as far as an actual cloisonne pins (like those sold in the stores for trading) those you have to pay for. I think this year they are up to $14.95 when you register.
Crowds will be a toss up. Usually it is ends up being greatly affected by when NYE falls and when school vacations wrap up. Every day after NYE the crowds go down, with yet another drop after the Marathon.
Hard to say. The 10k should start at 5:30. If they do a wheelchair start, first corral should leave like 3 mins later, and then it's like 5-7 mins between corrals. So corral A, done by 6:15ish, 10 mins through finish area, on bus by 6:30, should be at your hotel by 7-7:15. If MK doesn't open until 9, you could potentially make rope drop. But if you end up in corral E, then you might not even be starting until 6:15. If you are in E, I'd expect you to be taking over an hour to finish, so not done until at least 7:15. Through the corrals/bag check by 7:30ish. Then it's getting much tighter, you may need to wait for a bus to get back, and then you may not even be at your hotel until 8:15. Real tight to shower, and get a bus to MK.