I am glad to see you considering the weight balance--many don't. I sweat over the same issue with my little bus and did the best I could to even things out. Over the years I have driven various types of equipment where the weight distribution was way off. The result was unexpected reactions to seemingly normal operation which is very freaky.
I'd bet our buses are about the same length. Mine is 22.5 ' bumper to bumper with a 156" wheel base. Fortunately my fuel tank is centered directly behind the rear axle. Because of this I was able to put a 15 gallon propane tank and a 60 gallon fresh water tank on the left side between the axles and a generator and 40 gallon grey water tank on the right side. My 27 gallon black tank is centered behind the fuel tank (30 gallons).
The following tare measurements reflect empty tanks (fuel tank full).
Total tare 9820
Front axle 3930
Rear axle 5890
L side 4630
R side 5190
While my GVWR is higher than yours, the ratios should be similar. With my fresh water tank full the weight balance is nearly perfect. I was concerned that the grey tank would fill more than the black tank (relatively speaking) and that the emptying fresh water tank would go light and throw the balance of the bus off. After 4 years of use I have yet to notice any imbalance. Try your best to get things to balance out as you plan your build and then learn it's nuances. Jack