Ohh, lots of things to say.
1) I like the coloring of this MOC and the cabin does remind me a lot of the L'Orient! I think the Endeavour was actually yellow and dark blue, but black is a good substitute given how rare dark blue is!
2) it looks like you have some large cannons up on the main deck, are those the ones you got from the indexes? They look mighty powerful!
3) Your crew torsos look good, as well as the custom East Indy flag.
A few recommendations if I may...
1) I might move the mizzen (rear mast) back several studs and the Main mast (middle mast) back a few as well! They seem a little cramped in there. Mast position has been an issue for many of even the experieced builders, so it is pretty common to get them a little cramped the first time out!
2) The masts also seem a little tall to me, but it is hard to work with the fixed Lego rigging sometimes and achieve a perfect height!
As for the land based MOCs, they seem to get people from other areas of the forum more excited than ships, so posting one of those could bring in some of the admins and fellows from the history and castle areas as well for comments and praise!!
As for help with your construction requests... I can only show you what I have tried. I will give you links instead of pictures so the MOC focus stays on your excellent ship!!
If you take a look at the Arbiter II here you will see I used a Lego "Ilet" and a round stud to attach the jibs in three places. I then used a piece of string and a thin technic lift arm as a slide the could loosen or tighten the string at each point the sail is attached.
Take a look at this post where I explain what I did with some better close up pictures! Link to the Ilet discussion
and the Phantom uses the same idea here
The benefits are that you can move the jib around and still ensure that it stays tight and doesn't slide down the string and it will also allow you to angle the jib in any direction you want since no two points will be connected in a straight line as you have done in your photos!. I think it works well!
As for the capstan, Phred has a pretty complex one on the DDW (Dame du Loup). He might be able to give you a few pointers! Link to the DDW here
I also have a functional... but poorly placed capstan on the Phantom. I am not sure showing you the construction of it would help as I don't think it is a very good design! Here is how it looks from the forecastle at least. Capstan
See these MOCs and MORE in the Guilds of Historica!
Trian Burress of the Guild of Avalonia
Commander of the Capital, Watchtower Champion, Inventor of the spy glass!, Siege Expert, High Chief of Agriculture, Lord of Mesodraconem, Sir Gawain, Prince of the Forest, Finder of the Elemental Earth Crystal, High King of the Elves, King of the Castle, Elemental Terror Champion, Mystical Sanctum Champion