12. Repeat the process for the other countries with one exception. At step 10 and 11, create a temporary layer above the Countries Border layer for the stroking and spill deletion, and then merge down the temporary layer into the Countries Border layer once you are done.
13. Doing the sea isn't any harder. Just go to the Land/Sea Solid layer and select the Sea with the fuzzy tool, the use the same method as you've used for the countries.
And that's it. Easy peasy.