There are a couple different ways you can skin that cat. lol
Yes you can install a CSV125 or another CSV1A prior to the first tee. And yes you can leave the CSV1A where it is, just need to tighten the adjusting bolt a few rounds so it doesn't do anything. This way the CSV1A is just being used as a manifold for the tank, switch, gauge, etc.
Or you can install a manifold in the house for the tank, switch, gauge, and move the CSV1A outside and put it in the valve box before the first tee.