Huh. That's one of the parts I enjoy most! There's so many ways to approach it.

One I haven't seen documented widely:

Use a slow belt holding two science types (one each side) to feed the left side of a faster belt (which then has a left lane that alternates between the two colors). Repeat for the right side (your fast belt now has four colors). You now have a four-color belt to feed your labs, but it backs up when you use more of one color than another, so at the end you add splitters to extract the individual colors into four belts, and feed them back into the start (with priority, so they don't block).

Inserters can be used to place or remove research from the research facilities. For me that meant setting up the research facilities in rows, then having inserters pull some types from the top side downward, and other types from the bottom side upwards. Along with the large inserters there was more than enough space to build things with only a few belts feeding things.

That's likely where you start running into resource distribution and dependency issues, you might be subconsciously feeling the weight of the upcoming feature requirements!

For me the research was the only reason to keep playing as it gave purpose to the factory, otherwise it was just a factory for it's own sake. Same way a vehicle building game is a bit pointless without something to do with the vehicles, which Stormworks does a good job of solving by giving you rescue missions of different types to perform with your creations.