Everything is interchangeable providing it's the same ohmic value.
You're stretching over to that "other" forum we sometimes look at. I believe Peggy is a believer in the saniflex.
Yes, You plumb the Raritan directly into the existing holding tank, remove all the Vac stuff.
Been using wema/,kus gauges on my Viking for years, absolutely nothing to worry about.
You can get Stainless units at McMaster Carr, they have a very didd range and excellent quality stuff.
I must admit that a fresh water boat has significantly less maintenance required. I'm still running original air units, none of the engine cooling...