Nice game! It got me thinking about the best way to increase my numbers quickly, mostly by adding first then multiplying to get a big score. I was pretty consistently able to score 3-4k points by level 3 so the score to pass the levels seemed a bit low in my opinion.
I also wasn't sure what use the multiple sources were, I mostly used one each level and tried to bulk it up to the max. If there was a way to merge paths (two paths go in, one goes out) I would have used them more. The one time I used them was to add 'pressure' to my high numbers from behind by routing the unused sources into the path I made so all the produced numbers would push the rest, so that was pretty interesting!
This was very fun and satisfying to play. Great job!