Western Panama has the upland climate of Costa Rica with the better roads.. David is the provincial capital but the cooler highland cilmates of Boquete, Volcan, Cerro Punta, Bambito, etc are much nicer if the humidity bothers you. You end up with highs in the 70s, lows in the 50s pretty much year-round. Even up there you aren't that far from the beach. The main problem is that it has been pretty much discovered by expats so the prices have gone up considerably.
Among the big advantages in Panama for US - the country basically uses US dollars for its currency, no exchanging needed. They do mint their own coins in the same sizes and denominations (they will even work in the same vending machines), you almost forget to swap out your coins when you get back. The bills are US bills. This dates back to the canal construction.
However, the vast majority of the business and work to be done there is in the capital, which is at sea level and much hotter and more humid. You also have access to better medical care there than in the "interior" (which is what they call anywhere that isn't in the middle of the country since odds are that is where you arrive). Most of the work in the highland regions is agricultural or tourism-based.
as far as your note about no roads, the Darien Gap (Panama's eastern province and the adjacent area of Columbia) you do not want to go there. That gap is the largest tract of jungle they have left, and anywhere a road is built the jungle disappears within a certain distance as people move in to those lands. The areas that remain (out past Yaviza or so) are dangerous, FARC sometimes operates there, and people have been kidnapped attempting to traverse it.