Best of luck with your project, I like paths, all sorts. No matter where I go I end up walking, and paths will get you there.

Two items that I know you're already addressing but have come up as paths are developed here in the PNW: speeding cyclists, and incursions on private land. On the Burk-Gilman trail, the path has become a prime commuting route for cyclists, some of them moving too fast, and collisions happen with pedestrians, and occasionally cars at intersections. Fair's fair, you'll want to ensure safety of pedestrians just as you enforce traffic safety with vehicles. Also in urban areas the trail can attract some crime, such as robberies and rape - watch out for trail design issues that would make that more possible, such as surrounding brush and other places for assailants to hide. On another trail that took over a railbed between Issaquah and Redmond, the old rail bed ran smack dab through dozens of existing waterfront homes, which had gotten used to the lightly used rail line but are adamantly not happy with more frequent cycle traffic running through their front (or sometimes back) yards. What were once quaint lake side cottages for suburban dwelling middle classes had grown into multi millin dollar mcmansions, with resident lawyers, rich people and well-tended lawns etc. I think they're still fighting over re-routing parts of that trail, not sure - you'll want to be sensitive to adjacent property owners of course.

None of this is so difficult that reasonable folks can't address this in their own communities and contexts. Good luck!