You don't need to but #1 could be a bit easier if you prefer multiple torrent clients/instances for organization. qBittorrent / Deluge can run multiple instances so you could have like qBittorrent "A" instance pointing to your internal SSD and qBittorrent "B" instance pointing to your external HDD. That's just a quick example but I'm sure Transmission and other torrent clients can do the same.
The only tricky bit with multiple torrent clients is that they'd each need their own incoming connection port if you intend to be fully connectable (port forwarded). That may not be feasible if you're using a VPN that only gives you 1 port forward but otherwise it's doable, depends on your setup.