I've added a few things in this update:

+ Added an option in the config to add a required permission to use /ajParkour start (if enabled, will require ajparkour.start)
* Made it so the portal doesn't just make the player execute a command, will actually start it from the portal
+ Added start command argument to make other players start the parkour (requires permission ajparkour.others)
+ Added config value to adjust how many particles are spawned (0 will disable the particles)

Thanks to @starnos for the suggestions!