Looks like your figuring it out. It's all a matter of trial and error. Just remember that all the weight in the back will give you a tall steep but short wave and weight towards the front will give you a shorter but longer wave. If it was me i would get 2 400 pound sacks to move around. You don't have to always fill them all the way up but with the 155's you can't add more. You will be suprised at how much more weight you will want to add as you progress.
Happy surfing