Go trough the file and remember what is the smallest and largest number in each column. Something like this (untested):

my $min_col_2 = 1_000_000; # Something large enough
my $max_col_2 = 0; # Something small enough

my $min_col_3 = 1_000_000; # Something large enough
my $max_col_3 = 0; # Something small enough

while(<>){
    if(/^ZZ/){
        my @array = split;
        if($min_col_2 > $array[1]){
            $min_col_2 = $array[1];
        }
        if($max_col_2 < $array[1]){
            $max_col_2 = $array[1];
        }
        # Snip
    }
}
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To get the step size you also have to remember the second smallest number, and look at the difference between that and the smallest when you are done.