1. If you haven't completed your Bachelors degree, going enlisted is your only option. I highly recommend enlisting first, then applying for a direct commission or the Green to Gold program to finish your undergrad degree. There are a lot of options and you can benefit the Army while it benefits you.
2. Time commitment if you enlist would be 6 yrs active reserve, 2 yrs inactive (if you do not ETS). I can't answer this one if you were an officer. I think there are other year options available though.
3. I recommend joining now, unless your priority is completing school first.
4. In my first 6 years in the Reserves, I was gone for 8 months for Basic/AIT, mobilized for 15 months, and then deployed for 16 months, all involuntarily. I know soldiers that have been in for 10-15yrs and never mobilized or deployed. Your odds are based on the needs of the Army, your rank, MOS, and unit.
Consider this. If you're enlisted and active duty, the Army Tuition Assistance will basically pay for the rest of your school up to a Masters Degree. If you're Reserve, you also have Reserve Tuition Assistance but if you're deployed or mobilized, you're on active duty and can use active TA. Got my BS degree with only minimal cost for books.
Another option is to finish your schooling and enlist or commission and have the Army pay off your student loans as a term of your contract. I know a soon to be soldier with $250k in dental school loans that won't be paying a dime for them and will be commissioning as a Captain after OCS/OBC with only a 6 yr Reserve committment.
Be sure you know what you want to do before you talk to a car salesman, I mean recruiter.