I'm afraid I'm going to have to dip out of this thread until more concrete / easy to analyze data is supplied.
<Parts list>
That CSED is 200A bus bar. It's in the specs that you linked, contrary to what you had said. This means that you cannot have any breakers on the CSED other than 200A to the next device, or a feed-through lug to the next device.
View attachment 259855
The subpanel is 225A bus bar.
View attachment 259856
The standalone 200A may not be needed, but I'm not going to draw this out & reason it carefully, since it could be wasted work without knowing how close it is to how it's installed.
<Reply to Hedges>
I agree a schematic (one line would be better than the vague English thus far) would be helpful to share; it would also disambiguate what you're getting when you communicate with the electrician.
What does doing it "off the books" mean? Is he working for you under a permit that you pull?
A “tap” (which has a specific NEC meaning, that is different from English) can come at several places. If you take off the service conductors from the meter, that creates a new main panel.
That English can line up (vaguely) with one of the variants described above, and there are no red flags.
I guess the next step is for you to send us pictures of the installation & draw your own post-facto SLD. Backwards way to work IMO vs having it up-front. 18kpv is typically used with an interconnection agreement, and in California you used to need to provide an single line diagram (not sure if this changed with the recent simplifications).