If you have a drip or a leak of more than 1 GPM the CSV will just keep the pump running and size of tank would not matter. But with leaks of less than 1 GPM and times when so many people are using the water, a PK1ALT would be best. The LT is for Less Tank, as it would be best to pick up a 20 gallon size tank locally to save on freight. A Water Worker brand tank in about a 20 gallon size is good. A 20 gallon tank only holds 5 gallons of water, the same way an 80 gallon tank only holds 20 gallons of water. With the CSV the tank is more a mechanical timer than for water storage. Your water comes from the well and pump, not the tank. With a 40/60 switch, CSV set for 50 PSI, and a tank that holds 5 gallons of water, the pump will run for 2.5 minutes to refill the tank from 50 to 60 before shutting off. It doesn't start this 2.5 minute tank fill timer until the toilet is full, the showers are off, and no one is using water. With several people in the house, someone will use water within this 2.5 minute time, the pump does not shut off, and the timer starts again. It is very common for the CSV to make the pump run continuously 30 minutes to 2 hours, during times when people are home getting ready for school, work, or later to bed. This makes the pump only cycle once when it would normally cycle many times, even with a large pressure tank.
You will lose a little pressure through the filter and distance to the fixtures, so start with at least 40/60 and the CSV1A set to 50 PSI in the PK1AKT kit. Also make sure there are no hydrants or water lines teed off prior to the PK1A kit.