When we were researching, we were advised against a partial sunk above ground pool. By both the installers we called (they stated that they get a lot of business from issues with them) and the retailers told us unless the pool was rated for it, it voids the warranty. They didn't recommend it either.
As for wall and cove foam, we did both. We called 3 different installers and the ones who were in business the longest, with the most experience were the ones we went with. They recommended we do it. The cove would prevent washout in case of any leaks or other issues. But the wall foam actually protects and extends the life of the liner. We went with the thickest liner as well, but making sure we get the longest life out of it was worth the extra cost up front. He also explained other benefits too. Something about condensation and ice in the winter that I didn't understand. We got both and the spray adhesive direct from Gladon.