My first question would be, are you familiar with programming games? I mean, have you already created something before?
Because if that is not that case then I would not recommend starting with opengl. Why not try 2d first. It's easier and it will give you a good understanding of what it takes to make a game.

The "nice big fat manual" suggests a really large project, perhaps a difficult one as well. One that could easily take a year or two to develop. So why make a difficult project even harder with an engine that is hard to build as well?

Perhaps an 2d isometric engine would fit your current plans as well. There are a lot of resources on the Net about those and probably even more people who can help you with coding problems.

Anyway, those are just my thoughts

PS. I like your site. The only thing that bothers me is the menu. It's very slow