Hey, Well it's all personal preference, and desired flavor.
I brine, see below.
As for spice be sure and try it everyway possible. plain, just brine, plain with spice, brined with different spice.
I once did six half fillets all different way's and found. I and most of my friends liked the brined and dusted with just fresh ground black pepper. ( we did that, and - Just brine - just smoke - brine and old bay - brine and cajun - and brine and a blend of spice rub. They all were good but the black pepper was the best.
And I always do fish with Alder Wood, But if not available use something light. And you just need to smoke it long enough till it will flake apart with a fork. Or go by temp if you really want to be spot on. Fish I always go by touch and flake test.
Smoker temp I like 200 - 220 Deg
Dave's Fish Brine
2 Qts water
1 Cup Canning Brine Salt - And Qty may be different if you use some other salt.
1/2 Cup Brown Sugar Packed
1 1/2 oz Fresh Lemon Juice
1 tsp Garlic Juice or Garlic Powder
1 tsp Onion Juice or Onion Powder
Dash or two Tabasco
1 Tbs Molassas
Dissolve all in the water and chill. Soak the fillets 6 hrs or more. Be sure the meat side is in contact with the flesh. I put in a small cooler with a cleaned rock to hold it under. Add ice to keep it cold