1) How many other TransAmers did you meet along your summer TransAm route ? How often did these cycler interactions occur? --- I'll be traveling solo so it will be nice to meet people.
As Pete said, you'll see touring cyclists coming the other way every few (1-3) days. It's easiest to stop and talk when you're on relatively flat and narrow roads. It's really hard to have a conversation across 4 lanes of traffic, and neither you nor they are likely to stop on a good downhill (the one going up is always ready to stop, but it's tough to stop bike plus load when you're screaming downhill at 30-40 mph).
You'll also have lots of other chances to meet people, at picnic areas, campgrounds, diners, restaurants, grocery stores, gas stations, and just about anywhere else you stop.
2) I have the ACA maps, but does anyone have a resource to determine the best campsites along the route? any info or link helps.
You'll notice the ACA maps lists lots of places you can camp. Most of those will be great places, a few are more emergency /"I need a place to throw down a sleeping bag" spots. Some of the places I remember most fondly are town parks -- no scenery, birds wake you half an hour before dawn, but wonderful townsfolk. How will you determine what a "best" campsite is?