I'll give this a quick shot,until the real fishermen show up.
We get a lot of great yellowtail tuna here and it is presented like a medium-rare boneless NY strip steak....Nice crossed grilled marks and a seasoned butter sauce.
If you want to smoke it,I'd skip the brine, brush with a little olive oil, and I like some cajun seasoning.
Pam your racks and smoke at 180� to 160� internal.
If serving as an entree,I'd pull it by 150� as a fillet.
If it is as snacks, I like 1 in. thick by 1 in. wide strips....Easy to handle and better smoke absorption.
Hope this helps a little.