Sounds like a good idea, along the lines of car racing sims that have the racing line that you can toggle. The only hard part is that the lane sizes aren't fixed, most of the rules define lanes based on the width of the boat. I may try and implement this when I start working on the course map overlay.
There likely won't ever be a way to paint the boats in game. Photoshop and Gimp are much better tools than anything that I could ever come up with. I was a little hesitant making it so people could add paint schemes this early on, since I am planning on eventually creating a new boat model for the Unlimiteds.
Anyway, there are Photoshop templates for painting the current boats, if you're a graphic designer it shouldn't be too difficult, its just a matter of exporting them to the correct DDS image format.
More race courses are definitely planned.
Yes, I would like to make it so the boats can be setup differently. I'd think of the current boats as just a place holder right now, I have some ideas for trying to make the physics more realistic as well as adding the ability to setup different parts of the boats.
Unfortunately, I'm just one guy working on this in my spare time.
Feel free to leave any ideas/suggestions you may have.