Salt - Use Pickling Salt or Kosher Salt - it makes a difference.
Go easy on it. You don't want salty saltwater fish.
The amount of sugar to salt per approx 2 liters brine (water, possibly some wine, soy, maybe hot sauce, spices, whatever you throw in), is generally about 1/3 cup salt to 2/3 cup sugar... you aren't preserviing the fish - so eat within 4 days. Freeze after smoking is an option.
Use demerara brown if you can.
I brine from 8 - 24 hours.
After tacky, light light light spicing As far as skin... oil the rack, skin side down.
I take the skin off after about three hours... it usually peels off.