I suggest that you extensive research first
Overall, I believe your strategy is one of the worst.
Keep in mind that calling and asking if there is availability at this exact second may result in nothing available the next second. You cannot rely on a phone call unless you are ready to buy the ticket now. This is a very basic rookie mistake as inventories and pricing whether cash or reward change thousands of times per day.
Delta is one of the worst airlines for award availability.
Time for you to start reading the invaluable insight available not only on FT but all over the internet.