Pirates just gotta have a base. Where else can you bury your treasure
I've got some basic Pirate buildings made. I could e-mail them to you for your modification. My thoughts were to give them some new buildings that were cheap and performed a lot of functions so that you wouldn't be tempted to build the regular types.
Creating a whole tech tree is a pain though. More than I can do in a reasonable time.
I have created some special techs and the Pirate racial trait ( I'm as imaginative as you are
) I'll be glad to give my ieas to someone who has a little more know how than me. Just my ideas and I have never tested them.