To get rid of the "div by 0" problem, have each of the formulas in these cells (or all cells) first refer to the first collumn that you start putting info in and if that collumn has nothing in it then the cell in question can display "0" eg.

=if(a1=0,0,formula)

where "formula" is the equation you want worked out

Then, when your "Max" and "Min" formulas work something out "zero" will obviously be lower or higher than the other amounts.