Your pics are now accessible. However, that topo map is very difficult to read online.

You are going to be spending a lot of money to build a levee/dam that long! You almost always get the biggest bang for your buck building the dam where the contour lines come closest together.

At the current location your pond is only going to have a small area with a depth of over 8'. I assume you will be excavating the pond basin for the dam material, but that is still going to leave a lot of the pond at 4' or less in depth.

As regards the spring, most people do NOT cover the spring in the pond if the topography allows room to avoid that. A spring can function as both an inlet and an outlet for water from the pond.

I would recommend moving the pond farther to the NW, downstream along your existing waterway. You can build the dam a little higher there, and still impound 2-2.5 acres of water - and your total yards of material moved to construct the dam might be significantly lower!

I would definitely prefer to leave the spring slightly above the normal pool level of the pond. That way you can observe the water flows from your spring. If the spring is flowing, but the pond level is going down, then you know you have a leak. Likewise, if the spring dries up during the summer, but the evaporative water losses in your pond are acceptable, then you don't have to spend the money to drill your water well.

Good luck on your new pond project! I think the house on the hill overlooking the pond in the little valley will be a great view.