Progress update:
I purchased about 350 passengers which are all now sitting in my 6 car MTH Amtrak Premier Superliners as well as my 10 car MTH Rail King Union Pacific streamliners.
Hot glue worked great for seating the little people.
I bought the seated passengers from several sources, including the Chinese ones from eBay and Amazon. I also splurged for two packs (24 each) of Lionel's seated people for their 21" cars. Of course the Lionel guys cost 10 times what the others cost, so they got premium seats in the vista dome cars, etc.
Using John's LED lighting regulators and the LED strips he recommended, I converted all of the Rail King cars and they work great!
I discovered some soldering skills I didn't know I had while wiring the regulators.
Thanks again for all of the great advice and guidance I received here!
Stan