A couple other considerations...
Depending up on how your room is heated, you may have temperature stratification in the room in which case the tanks on the low rows will be cooler than those above. Putting fry in the low rack will mean they will grow more slowly than if they were in tanks on the top row. The same principle applies for spawners; they will spawn earlier and more often generally speaking if they are warmer than cooler.
Also, it'll be much more efficient and visually pleasing if your racks are constructed with tanks of the same dimensions, especially in each row. It'll be easier to do maintenance and if you have a leak or other need to remove a tank, it's always better to have a clean, ready-to-go spare tank to plug right in of the same size and not have to find other arrangements for the fish involved.