Stainless Steel Tank and Copper Plumbing

New to the forum I am, and have a unique application. I have a heat pump (free heated water) and have a super insulated 170 gallon stainless pressure tank that I want to store heated water from H.P. and a future solar-tracking collector. This is a used water storage tank in great condition. It will have a large expansion tank and t/p relief valve on the unit.

My questions are:
1. What is the best connection between copper and stainless for corrosion-free longevity?
Dielectric, brass, what? No galvanized, right?

2. I am estimating water from solar to rise to 120+ degrees. With no real heating element in the tank, do I still need some kind of sacraficial element (rod) in the stainless tank?

You could use either Stainless or copper flex water heater connectors.

Copper can be directly connected to SS without problems. The only time you'd get corrosion is if the thing wasn't put together properly and it leaks, then the water may leave mineral deposits when it evaporates.

That sacrificial element is called an anode, and I don't see the need in a stainless tank.

The anode has NOTHING to do with whether there is an element in the tank or not. The tank material determines whether you need one, and as stainless tank should not require an anode.