I'm not sure how many level, but I do knew max Fleet supply cost 75% of your income credit, and that's not funny! anyway, in most general game and common game, when your stop reseach for fleet supply> 4 or 5, stop at 50%, only upgrade if you have lot of income and full of fleet and see future if your fleet somehow lost and can recover quick aback in full force soon before enemie keep pound your empire?