I'm not a Gettysburg travel agency, and I don't have much trouble getting into Gettysburg because I live relatively close, but living nearby gives me a better perspective on the transportation issue.
Gettysburg is centrally located, so you have a choice of airports: Harrisburg International, Baltimore-Washington International, Regan National, or Dulles International. The one closest to Gettysburg is Harrisburg International Airport. The other three are in Washington, D.C.
If you want to fly yourself in your private plane or jet, the Gettysburg Regional Airport is located 2 miles west of town. (Opens in new window.)
Unfortunately, the downtown train station that Lincoln and eleven other presidents used is now a museum.
The nearest Amtrak station is located in Harrisburg. The Keystone line runs from Harrisburg to Philadelphia to New York City, and the Pennsylvanian line runs from Pittsburgh to Philadelphia to New York.
Greyhound has an office and regular route stop in Harrisburg. Their number is 717-255-6970. To get from Harrisburg to Gettysburg, you need to rent a car or hire a limo service. Once in town, you can continue your Gettysburg travel by bus on a Gettysburg tour.
You can find directions for how to drive to Gettysburg on Mapquest here. (Opens in new window.) There are several Civil War trails you could follow through Maryland, Virgina, and Pennsylvania if you wanted a larger perspective.
That's easy. There are a variety of options. To learn more about local Gettysburg travel, visit my local transportation page.
The tougher question...
That's up to you. The Gettysburg Convention and Visitors Bureau recommends 3 days. I think you could find enough around the area to keep busy for a week. A week might be a better idea so you have more days to choose from for outside touring incase of bad weather.
You could also combine a Gettysburg vacation with a trip to the Lancaster County Amish country or head south to tour Washington, D.C. Each of those trips could take a few days if you wanted to see a lot.
Or if you live close enough, as I do, you can pick one place in Gettysburg to go and only spend a few hours before returning home.
Basically, it's up to you and your schedule!