in response to #2:
I just hit notoriety of 8 and now have a quest to have a dagger made for me and then I'll be taught how to use it. (I was told to go see Elizabeth Swann as soon as I hit 8 notoriety and that began the string of quests)
in response to #3:
My cutlass lvl is I believe 7/8 I've 3 "moves" that can chain and the special. So far nothing else has "opened up" for me to learn. As my skills increase more abilities have been opening up. Just be sure to hit "K" to cycle through and make sure you use those ponts if you've got them.
in response to #4:
Well I believe it is sort of a "level" indicator. I've noticed certain quests becoming available at different notoriety levels. And "mobs" tend to drop in "con" (grey,green,yellow,red) when my notoriety increases.
Hope this helps and hopefully I've been accurate, it's getting late for me.
Stay out of jail!
-SH