Nice! I did some of that for a couple commission maps years ago... but mostly not directly onto the map. That happened once with an Iceland map I did in pen and I had to do it over a few times because of mistakes. So for one project I lettered all the written words for the maps onto paper and if I messed up a letter I just did it again in the word until it looked ok and then continued and edited it all in photoshop and placed each word where it should be. Then later I just lettered the alphabet with a few options for some letters on paper then scanned and built the words in photoshop using the individual letters. Practicing until I got better probably would have been a faster process though.