Charlie,

You have an interesting situation. On one hand, I agree with Theo's point #3....you can never have enough topsoil. The interesting point, is your comment that the more topsoil you remove, the more water you hit.
Here is one thought I had. Without knowing the goals of your pond and given your geographic location, I'm going under the premise that it will be a traditional bass/bg/catfish impoundment. This assumption may be a big mistake so please correct me if I'm wrong.
It seems that a good portion of southern pond owners incorporate a fertilization program in their pond managment regime. For ponds that have high flow through, fertilization becomes more difficult. If your plan is to include a fertilization program, perhaps it would be prudent to limit the amount of water flowing into your pond by leaving the topsoil in place, thus reducing the amount of water/number of springs.