A 3HP cannot take as many cycles as a 2HP or smaller. And the 3HP needs a minimum of 3 GPM to stay cool, which is why you need the -3 CSV instead of the -1. This also means you will be filling a pressure tank at 3 GPM instead of 1 GPM. All these things mean you will need a larger tank, but no where near as large as without a CSV. I would use maybe a 44 gallon size tank with the 3HP and the CSV125-3. Without the CSV I would use at least two 86 gallon size tanks, and cycling would still be a problem.
PS; When you have a 3.5"-3.9" pump in 4" casing, you just have to make sure the pump is set above the screen or perf where the water enters the casing, so the water flows past the motor before going into the pump.