To weight a 21' DD for surfing you should look at adding at least 1100#. More is better but use water ballast and not metal. Fly High make a 'Fat Brick' with handles at 155# that you can move quickly to adjust the loading while you figure it all out. The weight should be primarily rear and on the side you are going to surf on. Getting list in the hull is very important. You ride at about 11 mph but you need to work on it to vary the speed and location of the weight to get the right shape of wake and enough drive.
Basically you need more displacement to make a bigger wave, or a bigger board to ride the wave, or more skill to stay in the wave. Getting a big board is the easiest. You want to try to keep speed accurate as that changes the wave a lot. Don't spend time trying to be macho and drop the rope too quickly as that just means you have less time riding to learn your balance and build skill.
It's fun and easy on the body when you fall. If you like it at all I would strongly recommend getting a
FAE to keep CO away from the rider and those piled up at the back corner of the boat.
I've never seen the Aztec in person but it looks like it would be okay for surfing.
