The only fixed cost re the carriages is the leasing cost, maintenance is hours and mileage based, frequency dictated largely by how many miles your sleeper operation undertakes and how many hours the stock is running. That's highly variable depending on how many services you run, how many vehicles each service has and what route(s) your services take.
I'll be interested to see your crewing arrangements and how all that meets health and safety based rest periods, drivers hours requirements and such. I'll also be interested to see if your portion working fits around existing paths and what other services, if any, are going to be withdrawn to make this all work.
If you're working various portions, how do you manage with fewer locomotives per service ?
Just admit it Patrick, you've had an idea, reality means it won't work, but at least it has been discussed.