I would go to The Boardwalk on a day you’re in Epcot. There’s a gate in World Showcase that will exit on the path to Boardwalk.
For Ft. Wilderness if you’re horseback riding or dining you can park at the resort then use the internal bus to get to the horseback riding.
As Deb & Bill said, parking at The Boardwalk May be difficult due to prox to the parks. So if you’re planning on going to Epcot it would be easy to combine. There is a fee for parking at all the parks. Resort parking for visitors is free, but has a 2-3 hr time limit, and parking is very limited at the Epcot and MK resorts.