You can get a Pside-Kick for $399, and it has everything you need. Pressure tanks are pricy, and the good ones are even pricier. The CSV will do a better job at reducing cycling than a half dozen tanks, so you didn’t need a very large tank. However, the CSV will work with any size tank(s).
Large pressure tanks are just another load for the pump to keep up with. With a 40/60 pressure switch you will just have to wait for the tanks to empty down to 40, then refill to about 57 PSI before the CSV starts working and you see the strong constant pressure you will learn to enjoy. With the small tank you would have seen the strong constant pressure before you got the shower temp adjusted.
The CSV still helps with large tanks, and it actually the best of both worlds. Ie; You have a few gallons of stored water in the tanks, the CSV still delivers constant pressure, and stops cycling which makes everything last longer. It doesn’t make enough difference to waste money on the larger tanks, but since you already have them, might as well use them.
The CSV1A is probably the best one for your application, and they sell for around $200.
And no other check valves needed except the one on the pump.