I was looking into that Hagstrom USB device and.....$170.00?!?! Is there a cheaper alternative?
For 108 switches or buttons, joystick axes, trackball input, and rotary switches? I'm not sure...

It's more than I needed, but it has more than enough button inputs, I needed a few more pot inputs, and there'll be room to expand a little. I thought of Leo's units, which eliminate the latching command problem, but needed more channels without spending a lot more, ultimately...and in my case, the latching-command thing may not be a problem.
To overcome the CPU clogging possible with several latching toggles, I plan to toss some of the (free) rotary switches I had planned for gear switch, flaps, fuel selectors, etc. and go back to my idea of making simple mechanisms that will trip momentary buttons (I got a bag of 100 of them for less than 50 cents each). A little fab work there, but it'll be easy, and not much more trouble than working with the rotary switches, in terms of mounting them, etc.
I have so much labor to do on this 'pit in general that I've been trying to minimize the electronics tinkering. I don't mind paying a little to save time and labor here and there.
I work with electronics a lot, but as a fabricator, I'm better with structural and mechanical stuff, and I can work pretty quickly on that stuff.
If the remaining toggles (master, lights, etc) cause a problem, I will then look into adding isolators.