I rode the Elroy Sparta trail this weekend - first time in two years. The trail is crushed limestone, but really it is compacted dirt with stone mixed in - sometimes as hard as concrete. Road bike tires would work ok IMO - 23's may be too narrow, but 25's and up should work OK. That is unless the trail is wet.
There were several campgrounds along the route - I have never stayed at any. I just rode from Sparta to Elroy and back. I had no issues with bugs - but it was just that one day, and I was typically moving.