Keeps 3 days refrigerated. Salmon is good cold in the bowl — reheating is what makes it dry and fishy. Cool the rice quickly and refrigerate within an hour.
Usually not — it's soy-based and most soy sauce contains wheat. Look for a tamari-based version or make your own.
Wet skin and a pan that isn't hot enough. Pat it bone dry, use a hot pan, and don't move it for the first 3 minutes.
Yes — thaw overnight in the fridge and dry it well. Cooking from frozen works but you won't get crisp skin.