Great work ascanius. Some rep coming your way soon!
- It's interesting to see the way you have spread out the fault lines on the map, creating a rich variation of huge plates, tiny ones and some in between. I like it a lot.
- I see what you mean about the giant circle of diverging boundaries. Looking at it as an outsider, it doesn't really startle me. As the crust is thinner along that boundary you could even have a ring of fire - mostly under water, granted, but a few volcanoes could pop up above the waterline on that perimeter. On the other hand, if you don't like it, then by all means follow your thoughts.
- I found out that assigning a relative velocity to each plate helped me a lot in determining the way the plates interact and what type of boundaries they have.
- As far as I understand it, in a subduction zone islands are formed on the plate that stays on top. It seems that your islands are on the wrong side of the faults as you have drawn them. I try to remember it by imagining the triangles as mountains, and the side of the triangles/mountains is the highest.
- I also see that some fault lines stop and don't connect to other fault lines. Some examples: the diverging fault in the north of the southwestern continent, another diverging fault in the north of the northwestern continent, and both a converging and diverging fault in the northeast of the eastern continent. Any idea where they're going, or haven't you made up your mind up yet?
Anyway, hope this helps.
Cheers - Akubra