Yes, I am considering expandability. I found this post:
https://www.moyermarineforum.com/for...ead.php?t=5040
where similar project was done on same boat as mine. I like how the batteries fit under the starboard bench. I think I will do just that and keep the starter battery close to the engine under the port settee like Neil have suggested. I have to think about battery orientation, so that both AGM and wet cells could be used. But all I need to do for that is replace plastic battery box with tie downs.