Are there certain trails that always have lots of people walking on them?

The paths are not crowded at all. Once in a while cross paths with someone. Some sections more frequented than others.

Depends on when you go, on a Saturday or Sunday morning we always pass several groups of people, individuals, and dogs when we do the Syline Trail but that's because we are running so we are more likely to pass and see more people. If you take your time you will encounter less people.

I always feel alone there. Maybe cross paths with 1 or 2 or an occasional bike

From my experience. It was never crowded at any point. Maximum like a family or two walking on the trails.