Multiple line do work, it’s usualy what I try to achieve but I can’t say whether its any better or more efficient than just one high frequency mainline connecting the lot as it’s hard to run a comparison.
As for connecting towns, I like to experiment with ‘fast’ and ‘slow’ lines. ie, one line would serve all stops but another on the same track would act as an express to miss out every other station. EG, Commuter= A-B-C-D-E. Fast line = A-C-E
It seems to work well but it’s usually at that point I had to stop playing due to performance issues.