I haven't had much finding a dedicated crew yet and so I find it's very fluid in using the matchmaker or even the lfg tool on Xbox. But my ideal setup is basically what op was saying.
Captain:
Makes all the decisions based on the info provided by his crew i.e. Where to go what to do and whether to fight
Calls out all desicions for naval combat
Stay with the ship at all times unless at an outpost and under certain circumstances
Steers the ship
Shares duty of aft sail with Quarter Master
Master of Sailing:
Tends to the map and relays his understandings to the captain i.e. Locating distance and direction to outposts and islands of interest.
Controls main mast, dictates wind direction and calls the for which directions sails need to be turned
Shares in duty with Quarter Master and MoA cannon fire when directed
Shares in duty with Quarter Master repairs
Stays on ship unless directed to
Shares in duty with MoS boarding action
Master of arms:
Controls fore sail changing in direction as MoS or Captain dictates
Main look out from the prow alerting captain of nearby points of interest
Keeps stock of canonball inventory and keeps cannons loaded
Calls out which side the enemy vessel is on
Shares in duty with MoS and Quarter Master
with cannon fire
Lead expeditionary making sure too grab everything not nailed down
Protects Quarter Master while he returns to ship with the booty
Decides tactics on land battles
Shares duty with Quartermaster in locating the aforementioned booty
Shares in duty with MoS boarding actions
Quarter Master:
Keeps stock of planks and bananas and the storage of valuables
First man to repair boat dictates wether MoS is required
Shares in duty with captain aft sail control
Shares in duty with MoS and MoA in cannon fire
Secondary expeditionary force
Shares duty in locating treasure and collecting supplies
Carries the treasure back to the ship and dictates storage
Can be used as secondary lookout from the crow's nest
But it never works out this way. I tend to not captain as I love navigation too much,but if I was this would be my ideal crew setup