Could I (maybe with help ) set up a command line that would load the same sketch into any Arduino that I connected to a USB cable??
So long as the boards are similar, it should work very well. I think the only issue is processor model (e.g. they all have to be 328s) and clocking (e.g. they all have to use 16 MHz crystals).
The IDE will actually tell you what the command-line is: just hold the shift key when you click upload. If you preserve the HEX file, you can use it over and over.