It doesn't seem like it would be that complicated. Here is a very generalized approach. Of course you'll have to fill in the subs as required:

use strict;
while (1) {
  my $run_ct = how_many_running();
  my $wait_ct = how_many_waiting();
  foreach (1..(10-$run_ct)) {
     launch_next_waiting();
  }
  sleep 20;
}

sub how_many_running{}
sub how_many_waiting{}
sub launch_next_waiting{}
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Hope this helps.

"Make everything as simple as possible, but not simpler." -- Albert Einstein