Reread your OP ... plus latest o course.
Unless ya changed it since. Then I missed some stuff. That is a nifty lil challenge you have going on there. Would stick by what I said above too and advise someone to stick with a more newb friendly Mint release. Who knows though you might love lmde and have zero problems.
Was just basing that on your having problems getting it installed via usb and saying ya needed a simplified "mickey mouse", how to ... etc.
This comps a dinosaur too and doesn't give me the option of installing via usb either. Came to the conclusion, would just have to be satisfied with what's available within it's capabilities. Or could perhaps go through the trouble of flashing/updating bios and hoping the mobo manufacturer for it had released bios updates that would support booting from usb in the time since this hardware came out.
Decided against it and went with option A instead. Just too much aggravation to go through and comp has a DVD-RW drive on it. Just ran out of discs for it atm.