It is recommended to rent a car to get around the destinations. There are car rental options available in Pittsburgh International Airport, which is about 30 minutes away from Houston, PA. Parking is generally free at the points of interest, except for Laurel Caverns Geological Park ($5 per car) and The Mall at Robinson (parking fees vary depending on duration).
If you have more time, consider visiting Frank Lloyd Wright’s Fallingwater or exploring the city of Pittsburgh. If you have less time, consider removing Day 2 or Day 5 from your itinerary.