There is a bit of the good, bad and ugly in this thing. I see the barnyard runoff looking water, but it looks like someone had a fairly good eye for the rock layout; it looks much more natural than the typical stack of round rocks used for landscape ponds. The face of this thing looks much more like a natural waterfall. See how the rocks are not all one size?
That site has a lot of potential too. Use the slope to make it look real, but avoid the "stream at the top of the hill" look of usual decorative ponds. build up around the water fall to make it fit the landscape.
If you plan to use a synthetic liner, it will need a lot of protection from the roughness of the boulders. We use clay so we don't worry about that. You can use clay under your liner in case you do puncture. It would be a huge pain to chase down those leaks.
In our experience, limestone is only a problem if a fish experiences a sudden change in water chemistry. This is also true for a host of other minerals, but that is a bit off topic here. We add lime to numerous projects for various reasons.
I am envious; you have a terrific opportunity for a before/after example here.
Love to see how it turns out!