only problem i can see with this idea of crew lvls with cost is that the more wealthy players can keep the high lvl crew. Were the less able to keep a high income is going to suffer from not being able to keep up. As an example you get enough money to get yourself a crew of able seaman. You end up getting into a fight and get sunk/captured. Now all that money is go. (some think well ok so what) You now have to try to grind out the money t get the "good" crew again but now you get ganked when you are trying to do missions or trade to make the money you need to get the better crew. You are now at a MUCH greater disadvantage wit hthe low grade crew if the enemy has top lvl crew. Now you get sunk and are set back EVEN more and the next thing you know you are stuck with 50% effective crew b.c you had a bad fight or 2 and couldnt keep up.
i think if it was more like
landsman 90%
seaman 95%
able seaman 100%
that way the player still has a chance to overcome the odds with skill.