There must be at least one marine store in Curacao that can advise you. As mentioned earlier, I like Amsteel Blue from Samson, but it is pretty expensive (the 5 mm line costs $1.05/ft)
APS recommends 25' Excel racing (5 mm or 3/16''); also expensive @ $1.20/ft http://www.apsltd.com/c-2396-sunfish-linepackages.aspx
I am late in suggesting this, but the first thing that I would very much recommend is making some connections with local Sunfish class members. Even if you don't race, just showing up at an event will likely change your entire experience with your Sunfish. I will go out on a limb and guarantee that local sailors will just about fall over themselves to help you with all of the issues you are asking about as well as help you with finding local gear and such.
Just Google "Sunfish Class Curacao" and you will find contact information, both phone and email. I see your local calendar lists an annual womens regatta there tomorrow. If they are still having it I would check it out. There will certainly be good local Sunfish experts at an event like that (and I won't state other obvious possibilities).
I assure you, you will not find a more hospitable group than Sunfish class members. You will have an instant sailing family. Again, even if you do not race in events or at least don't for awhile, there will be no faster way to learn and to address all of your questions. Also, if you are inclined, the views from the race committee or mark boats are unparralleled, and extra assistance is always welcome. But that is by no means necessary...just stop by any Sunfish event anytime and you will make new friends.
I was cleating the halyard to the cleat. But on the cleat of the boat not the mast. This because the cleat on the mast is loose. I will be fixing this or if not possible buy a new mast to use a slip knot and cleat it on the mast. This way I can keep it a bit more tight. Will take a closer look at the non stretch halyard. Mine is getting old anyways and it seems to be not a bad investment that could save me some trouble.
It is never to late suggesting to contact fellow sunfishers in the area. I did meet some and got some suggestions. Indeed they are nice and helpful and you can learn a lot just by talking to them. You are correct to guess I am not really into racing but just go out once and a while to relax and enjoy the water, sun and the wind pushing me forward instead of a noisy engine.
Thank you all for the suggestions and advice, seems like I always have an instant sailing family online