The Dobbin House has free tours each weekend starting at 10. They are free and interesting.
The museum and cyclorama at the visitor center is well done. There is a fee. 2-4 hours depending on interest.
The Seminary museum is also well done. Fee and worth 1-2 hours.
The Shriver House does an excellent tour. Fee and maybe 1 hour.
Jennie Wade house is a cool tour. Fee less than an hour.
I have been to the battlefield over 209 times in my life. Rain never stopped me from being on the field.
Good luck and I hope you enjoy your experience.