I use a @Start9 with their built in marketplace relay active and I cannot use it with my most of my clients. Only with @nos.social . 

I would ask the community, why not? Is there a security risk, to me or users? Must I use a domain connected relay with DNS management and am I opening myself to trouble by using my own .onion addressed relay for my own storage of notes and media and for others that follow me to snag that content without going centralized on a @primal @nos.social @damus or other branded relay? My thought is that true ownership is keys and data backups. If I don’t have my posts, what do I have? An empty key with followers?

What am I misunderstanding?

nostr:note1za57rgyzzv334gy8pdlsk3xvte4mhrq3ydqsa8h6ayq84cjdnvhs0gpu23 

 The issue with using a relay on your own home network and accessing it outside of your home, comes down to accessibility. You need a way to connect to your home. Several methods exist to poke a hole through your network. You eluded to both. You need TOR or another method such as Tailscale or a slightly more complicated method with port forwarding, an SSL cert, Cloudflare and/or DNS entries.