Overall, I think you have a pretty competitive profile. To answer yo questions:
1) I would say that this is the biggest hole in your app right now. I know what it's like to have to study for those actuarial exams, but admissions officers will still wonder why you don't have more community involvement. ("If it's important to you, you'll make time for it," they'll probably say.) It's impossible to say that you'll definitely get dinged because of this, but if you do get dinged this year, this would be my first guess as to why. Would it be possible for you to wait another year and get involved somehow now? Obviously, you don't want to do it (or look like you're doing it) just to get into school, but some is better than none.
2) I wouldn't sweat this too much. As long as you can demonstrate a good reason why you dropped out, and show that you're now very serious and dedicated to excelling in school, it shouldn't be a huge issue.
3) Don't worry too much about your undergrad school not being well known. Coming from a top school can help you, but I don't think that coming from an unknown school hurts you. And, adcomms are always more interested in what you did in school, rather than what school you attended. (The same goes for work... They want to hear about YOU, not your company.)
4) Three years of experience by the time you enter is a little low, but fine. It won't keep you out, especially if you have good leadership experiences to point to in your job. However, see my point in #1 above about possiblly waiting another year.
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