It depends on your risk profile. On a private tracker it is much less likely that copyright trolls sit in the leech and log the ip of every peer, which is the main reason to use a vpn on public trackers. But it still increases your anonymity if you torrent over VPN.
And If your isp doesn't allow port forwarding you could become connectable by using a VPN provider that provides that feature
If you use let's encrypt certificates on that subdomain it's pretty easy to find. https://crt.sh/