same as any remote. rclone mount remote: /path/to/mountdir
yes, this is a good template https://github.com/animosity22/homescripts/blob/master/systemd/rclone-drive.service
yes
are two rclone caches, here is a summary i wrote up
https://forum.rclone.org/t/status-about-using-rclone-for-music-storage-playback-in-2021-access-times-improved/27648/34