Air National Guard and reserves are very, very similar. The main difference is that reserves are funded totally by the federal government, while guard units normally get some funding from the state as well as a lot of federal funding. The reserves will normally only be mobilized for federal missions often overseas (ie war, contingency). Guard units can also be mobilized by the state governor, normally in response to natural disaster. Infantry, helo, and airlift units have an obvious role during a disaster...fighters, not so much. There are also cultural differences in the guard, and career progression may be slower and longer.
Yes, you can have a civilian job of any sort, and most folks do (there are some full-time jobs at guard/reserve units). Airline people have a lot more flexibility to do military duty than the typical corporate manager.
There are C-17's at March AFB in Riverside CA and the Charleston SC AFB, among other places. Check out baseops.net for more info.