Get the water tested and we can close in on a recommendation but a few question can be answered.
Be careful of grossly over sizing the system, it can lead to problems
I like the Fleck 7000 SXT and if your use is what you claim you will want a valve capable of high flow rates
Standard mesh resin works just fine 99% of the time but let's see your test results
Variable brining sounds good on paper but again, most times is not necessary.
Salty discharge water will destroy your sump pump in short order