Welcome aboard sir!
You're planning the same as I have planned for my car. I want to tap into the internal can bus in the car to be able to talk to the display in the instrument cluster (the original nav unit does this) in the same manner (or an extended manner) as the original equipment does.
So I think we might benefit of each others work!
Btw: There's already some obdII support in OM via a few different projects. JHeizer has more info on this.