Hey Mike, welcome to the forum!
That's a great first machine, can't beat the versatility of a USS-64, it can vend just about any type of can or bottle and it's a great size. I have owned a good 6-8 of them over the years and they are my go-to machine when someone is looking for one for the garage/basement/mancave. I'll try to answer some of your questions, but probably need some other info back.
First off, you may want to consider what your plans are with the machine before doing a full restore on it. The only reason I say that is there is generally a limit on max price that you're going to hit for the value of the machine. If you sink a ton of money into it, you might not recoup your costs if you were planning on selling it down the road later. Now, that being said, there have been some beautiful restorations of USS-64's by members on this site and they look great when they are done. I have one that I have used for the last 7 years as my go-to machine in my basement, and I eventually plan to do a nice resto on the outside of it. I plan on a dark Pepsi blue (mine is Pepsi branded).
As for the free vend issue, couple of things:
1. do the columns spin when they are empty? There should be a flap at the front edge of the cradle (on the inside) that sticks up and prevents the column from turning when empty. The previous owner may have bent those forward to get the free vend to work.
2. That N.O. switch that you found is part of the vending system, it is used to tell the coin mech to reject coins while the machine is in a vending cycle. See my photo for a pic of the bottom of the back side of the vending stack. There is a flapper (just below the left spring in the pic) that would normally prevent the columns from being turned. A solenoid pushes that flapper to the right when the coin mech receives enough $, and you would then be able to turn one column. The motion of the column then pushes the flapper back into position, again preventing the columns from being turned. The N.O. switch is pushed to Closed State by the flapper during the vending cycle.
Sounds like there might be some rigging of that mechanism that is causing the free vend. The stack is very easy to remove, take out all the shelves and remove the two screws in the top, you can then rotate out the stack, there are two pins in the bottom that hold it in place. Helps to have a buddy the first time you take it out, can be cumbersome.
On the coin mech, you are engaging the 'inventory switch' (red I think?). If there were nickels in the hoppers, they would be ejected when you do that.
You've got the right guy on the cooling system, there are a couple of compressor guys on the site and you can't go wrong with either of them, you will be happy.
Found two more photos I forgot I had, one of the vending during steady state, and the second of the flapper pushed by the solenoid allowing the columns to turn
