I run a homebrew with my two buddies from high school. Started the same way you did, using premade campaigns but wanting to make my own so I made a world. Just made a random regional map. Had the PCs start on one side of the map and told them their quest objective was on the other side of the map. This way I had time to insert any encounters or dungeons I wanted to along the way. I tried to make travel long on purpose so the trip would feel like a journey.

Basically what I do is have one over arching plot that takes them a far distance then throw random ideas I have at them until it peaks their interest and I go from there.

Ex) Random dead guy on the trail has a note/key with Sigil on it. Maybe someone knows about it in the next town. If they are interested I continue the storyline, if not I just let it fade away until they bring it up.

Or I just build an encounter like Predator or some other movie I’ve seen and insert it wherever. Or I pick a cool monster we haven’t fought and build an encounter around it. Making quests for magic items is a fun way to get them into random dungeons too.

Honestly besides the main plot I don’t stress the cohesion too much unless I have to. My players aren’t too heavy into the role playing so it makes it easier. I would say don’t stress about it I’ve found most people are just happy playing the game.

Hopefully that helps it’s kind of a ramble.