Your battery location should be fine. It's best to have them at the CG or around the rear of the sponsons, as you have shown with the red. If it's not shown on the plans, you want the CG to be between the rear of the sponson and the next frame back. You can balance the boat with the motor and radio gear to a large extent so I wouldn't worry quite yet. You have to remember, the only weight you're going to have at the rear is going to be the strut and prop shaft, rudder assembly and the tails/wing. I would get the tail mounts, rudder and deck installed AND THEN see where the boat balances at. If it falls in between the sponson transom and next frame back, you will probably be fine. If it's outside of that range, you will be a bit more limited on where to put everything. The strut and tail feathers won't weigh that much and should be offset by the prop's lift. You also have to remember, you still have a cowl to install though, like the tail feathers, it shouldn't weigh a lot either.
As for a thread on my Pak, not yet. I'll be starting one when I get a bit further along. Still debating on whether I should include pictures of the full sized boat or not, if for no other reason, for comparison sake