Asklemmy

You have to start smaller, and specifically, you need to plan on a minimum of fully redesigning the entire board twice, three times if you want to get it to a really good state.

You're largely guessing what will be the optimum configuration for routing. After the first work through, it will be obvious here major circuit blocks need to be routed to make the design work at all or, at least, make sense. The second time through things will fall in place much more quickly as you'll know where the major problems are and start by routing them. At this point, with a little experience and thought you'll probably see the last major issues related to things like ground loops and likely electrical noise issues that can be solved if you completely redo the design.

If you start out like this, you'll likely start thinking about your designs inside isolated little circuit blocks, like the power, analogue, digital, communications, sensors, etc. Then you can start simply redesigning these little blocks as needed while you also start saving these blocks in KiCAD and dropping them into future designs with minimal changes.

Once upon a time, I saw someone say "design is done in blocks" and I tried to start out like this, but that was ineffective for me. I needed to learn how everything fit together first and that made the blocks design methodology click.

Just as a few tips, make your traces as large as you can/defaults are way too small, make your through hole pads much larger so you can desolder stuff several times without lifting a pad, and route a ground trace through absolutely everywhere possible and connect it to as solid an infill plane as possible, use 0R connections to save yourself from mistakes in routing and add an easy location for pull up resistors. Finally, print absolutely ever design on paper with the back side inverted, and glue this to a piece of card stock like cardboard. It can be from any food packaging like a cereal box. Then use a drill or awl to make all of your holes, place your components, and check the fitments inside your project enclosure, this alone will save you MANY mistakes.

GL