So, I spent around 6 hours coding and finally managed to get a system working where you can have a single party member follow you around in the overworld.
There are some minor issues (such as them not following you if you initiate a cutscene, them walking up to you if you're holding the movement key up against a wall, them layering over or under objects based on the player position rather than their own position, and them briefly disappearing from the overworld when you transition scenes), but all of those (except for the scene transition disappearing, and cutscenes breaking their movement for the remainder of the room) are minor enough issues that I honestly probably won't even bother fixing them, especially since right now I've only planned for a single, brief instance (I'm talking less than half the first area) where you'll have a party member.
But yeah, there's now a functioning overworld party system! Even though it currently only supports one additional party member.

Welp, until next time, have a good one!

-KK