Wouldn't call this the "essential" guide, but here's some episode episodes I remember with him being a big or interesting part of. Episode 05 and 07 of Part 1 obviously, Episode 24, 55, 56, 61, 103, 108, 112 of Part 2, 05, 24, 26, 38, 47 of Part 3. Episode 10, 17 of Part 4 and Episode 16 and 18 of Part 5. Had to go through a few of these episodes on my hard drive just to make sure, and probably missed a few but I'd say these are a decent amount.
Part 5 also gives Goemon a lot of interesting development and even the last arc deals with how Lupin views him as a person, so you might as well watch the whole Part.
Can't say much for the movies but I know that The Fuma Conspiracy is a Goemon movie.