For the still (btw, sounds like a NICE find!!!)
DO THIS FIRST: Before firing it up, make SURE that it has the vapor path open. Make sure any tubes, lines, etc are not packed with some mud hornet nests, or bird nests, or other blockage. If this is so, and you fire up the still with a charge (even water), then it could be very dangerous, and possibly cato explode on you, due to building pressure.
If the still is it dirty on the inside, or just on the outside? Easy way to clean the inside is to run it. First do a pure water run. That will allow you to spot leaks. Leaks doing a water run are no problem at all (as long as you do not build pressure and 'explode'). However, leaks with ethanol, CAN be a problem, and dangerous. Ok, now after a good water run, it should have some of the stuff cleaned out. Then do a weak vinegar run. This will help to clean the copper some, but not do ALL of the cleaning needed. Once that is done, and you are sure the still is solid and leak free, and has no vapor leaks, etc, then run some cheap wash that you will throw away in the end. This IS the cleaning run, it will clean the inside out, and make it where the still will produce a clean drinkable product. NOTE do not drink this first run. Consider it tainted, and unsafe.
If the still is simply dirty on the outside, then use a garden hose, and scrub brush (plastic, must be solfter than the copper), and scrub off any dirty or other crud. Then if the still is green tarnished, or you simply want a 'shiny' clean, then use lemon and salt. I find a green 'brillo' pad, a bowl of salt and a bowl of lemon juice will clean up copper VERY shiny, very fast. Once you have the copper cleaned using an acid like lemon, be SURE to rinse if off well, to cut the acid.
NOTE if you remove the patina, it will reform. There really is NO reason to remove the patina. It is a GOOD thing. Now, if the copper has tarnished to the point of the powdery white/green corrosion, you probably should remove that. But the good strong brown or reddish brown is a good thing. It will keep the copper from 'micro-dissolving' into your product. It also protects the copper. The patina grows only so much and then becomes 'stable'. If you remove the patina, you are removing some metal. The patina WILL regrow, and if you again remove it, you are again removing metal. Doing this time and time again, you CAN wear out the still.
Like I said, it sounds like you made a hell of a find. Wish I could find a unit like that!
Hillbilly Rebel: Unless you are one of the people on this site who are legalling distilling, keep a low profile, don't tell, don't sell.