All achievements are legacy based---all of your characters contribute to all of your achievements. So, you could max out 2 crew skills on your main, 2 on an alt, etc., and it would all contribute to the one Master Craftsman achievement for your legacy. (The title reward would then be available to all characters as well) This is true for all types of achievements.
So do you need to complete all the crafting skills on one character to get the "Master Craftsman" title or is it based on legacy characters as well. Meaning, if I have various skills at 450 across multiple characters that add up to the total amount of skills in the game.