Make Your Own TorrentBox From a Pi : 10 Steps (with Pictures) - Instructables
Build an Always-On Raspberry Pi TorrentBox - Pi My Life Up
Update with guides and links, see comment) Pi zero for PiVPN & Pi-Hole; Pi 4 as torrent download station with PIA VPN mounted to Synology : r/raspberry_pi
RPi 4 NAS w/ Auto-Torrent (WIP)
Raspberry Pi-based Torrentbox With VPN, SAMBA Shares, Hard Drive Disk and Deluge : 10 Steps - Instructables