(First of all, thanks Karl! I hope you'll enjoy the game.)
To answer the scale question, yes, Black Scorpion's figures are noticably larger, but they're also slightly more slender than Crusader. Now this doesn't bother me, and since there are some lovely sculpts in there, I think it would be fine to use them as your more heroic captain types. Once the figures are on the table and in use, I think stylistic differences become much less noticable.
Black Cat Bases' pirates are about the same size as Black Scorpions. There are some fun figures in that line, if you want to check them out.