gas/electric dryer preference
"Can I assume the dryers are to be electric? Is one or the other preferred by serious collectors?"
I would think that in collecting, one couldn't be picky about gas or electric, and they perform about the same. For regular use, gas vs electric rates and/or the availability of gas service would dictate the choice. If I were collecting, I would end up with gas, since the gas service in most homes could probably support several gas dryers whereas more than 2 electric dryers would call for some heavy duty entrance service, especially if other appliances like ranges, water heating and heat-a/c are electric.
In our old house, for a test I once turned on all 5 burners, the oven and the broiler on the range, triggered the hot water heater, fired up the furnace, started the dryer, and turned on our pool heater, and there was enough gas flow to run it all through the original standard residential-type gas meter.