>If the field is defined as nvachar(...) you don't really need to add N' in front as the field still will be nvarchar. You need N' if you use unicode characters.
>
>sp_ExecuteSQL requires nvarchar parameters (Command to execute and Parameters Definition)

The declaration is:

DECLARE @Command nvarchar(4000)

So, at the end, if I have it or not, because of that declaration, it will not bother anything. But, as a best practice, I guess it would be better to keep it there.