Glad you've found the diagrams of use.
I agree what you are now proposing is now the way to go.
An interesting by-product of what you proposing is that by isolating the
"vehicle " wiring at ignition switch off, you are isolating all sources of parasite drain from the vehicle battery on the car bar a faulty alternator drain.
I think such a set up could well be a possible and very effective solution to the never ending problem of parasitic battery drain.
My only reservation to the set up is on turning the ignition off you isolate everything on the car instantly, no time is allowed for the car to go to "sleep".
At the moment I have no idea if this will cause a problem.
What you will probably find is that everytime you turn the ignition on you will get the Air Suspension Inactive message. Could get a bit tiresome having to do full lock to full lock everytime.
What other problems may come to light I hope you will advise us.
On the face of it, isolating the battery instantly is no worse than a "battery disconnect".
Time will tell.