Welcome Willie
Sounds reasonable on the surface, but a few points.
How long will your water source last @ 70 GPM?
You say static head of 55 PSI 70 GPM, do you mean 55 PSI when there is no flow (static head) or do you have 55 PSI when 70 GPM is flowing, there is a big difference.
Is there a possibility of your system freezing?
I don't see that your stand alone inverter has any place in your proposed system, it's too small to utilize that inverter, keep it for Ron.
I agree you will need an adequate dump load, in case usage is less than input, but I do wonder what you mean by "big power things", each Power Pack has a capacity of 1350 watts continuous, so load planning will be an important issue for a 51 amp hour battery even with continuous power input.
I find the chart here useful in hydro applications,
http://www.nooutage.com/powerspout.htmIt is smart to ask so keep us informed as your system develops, I have a good stream but it is also a bit like a woman, it has two extremes and no happy medium.