Sorry Tom, I'm already taken
Just use a spoonful or so of butter... If the butter already has lemon it in, then you are set. If not, let me know if you plan on using real lemons. Just throw on a good amount of pepper...
You can't really mess this recipe up! You'll add more lemon butter/pepper once you remove the fish from the water. The amount in the pan is just for a bit of extra flavoring while cooking.
I'd go for plain butter on the potato.
The fish doesn't get soggy. The water simply keeps the fish from drying out.