Having it in front of one return is fine, or you can split it up and put it in front of all you have. Your choice.

The 9 pounds of stabilizer come out to approximately 18 cups. Make sure you're keeping track of how much you're putting in. Give it at least 24 hours after the first batch is fully dissolved before testing; we want to be sure we've had at least one complete turnover of water.

Test strips really aren't very reliable and I'm hesitant to comment on your numbers. Will you have a chance to get a sample tested at the pool store tomorrow?