My math would be a bit different than yours
I'm not convinced that the LSL could really handle that large of a train.
And if you were to do that, I'd suggest something I've argued for years: Make the LSL a single BOS-CHI train and have a separate "21st Century Limited" that ran NYP-CHI along much of the same route, but say 2 hours later, with a few different stops (keep the major cities of course).
And again, with the Silver Service, I think you're better off with a 3rd train.
But, I'll give you that, let's say we follow your plan... if you're buying 70, might as well buy 100.
(and part of my idea for a 21st Century Limited would be that since a large portion runs through NYS, NY fund it and run it with NYS themed cars, especially the diner.)
I really don't think the Twilight Shoreliner could support that many sleepers, but again I'd like to be proven wrong.
It's a all dream though (much like the ones I have while sleeping in my Amtrak sleeping car)