Yep, you will be an O-2 for 2.5 years, as it would be tough for you to compete as you move up with evals starting at O-3.
I can speak of the missions we do as C-130 pilots, but can not really give you your chances on making a switch from the USAF to the USCG, Coastguardocs.com will probably give you better info.
The missions you will fly are SAR, LE, migrant interdiction, counter-drugs, trash-hauling (especially in AK), homeland security and a few various others.
There are only five places you can be stationed as a C-130 pilot, and they have a few quirks associated with them:
Barbers Pt., HI (Long-range SAR in Pacific…Guam, Kwajalien Atoll, Tarawa, LE deployments out of American Samoa & Guam)
Kodiak, AK (Logistics resupplying other units in AK, Fisheries)
Sacramento, CA Fisheries)
Elizabeth City, NC (International Ice Patrol...super-freakin' cool).
Clearwater, FL (migrants, migrants, and more migrants)
Some units average 25 hrs a month, some average 40+ hrs per month. You will have plenty of time with your family as the longest you deploy is typically 2 weeks, however you will have to spend the night at work about once a week as part of a crew that is ready to launch w/in 30 mins for emergent SAR/LE, etc. If you have it on a Saturday you will have Monday off, if you have it on a Sunday you will have Friday off. There are days you have to work long hours doing test flights or paperwork (like in any service), but it usually goes in cycles. And many times while I am on duty, my wife will come with the 2 kids and bring me dinner, and we will hang out for an hour or two.
If you have specific questions please PM me.