A lot of cc don't have a ton of space in the rear of the boat. The overhang will be nice, but you only need enough to let the water run off, and not down your back when under way. For shade get a good hat! I love my hard top, never have to wear a hat anymore, but it can get in the way when casting a lot, but I do most all bottom fishing.
As far as a crows nest, It has been done on the V20, and we have seen some pic's, but know one has ever said how they go?? I would think a small lower type might not be to bad, but if you make one to high you going to have issues. You know what would be nice, a sunroof in your pilot house with a small ladder to step up on, stick your head out the top and get a great view without building anything to high?? Just popped in my head as I am typing.
Whatever its coming out great!! Keep it going you have a whole winter to go before you need it.