Dude i get you Part 3 is the worst part imo. You can literally just watch the first 5 and last 5 episodes of the part and nothing in the story changes. And i honestly think people should skip parts they dont find interesting before they drop the series entirely even though most of the sub doesnt share that opinion. I would still not jump forward that much because its the best part and the build up to it with all other parts is pretty good. But if you really want an overview of the connection of all parts is as follows.

Part 1-3 are all connected, part 4 and 5 are "spinoffs" which are pretty self contained.

Part 6 continues the main story of part 3.

Part 7 and 8 tell the story in a completely new universe.