You might try rubbing compound on the rust and see how it does (small section,if possible not on the rails to start (cleaning the side of a rack would work). IF that removes the rust then you have a solution to the rust problem and hopefully can restore the rails. The carriages need to be inspected and if they have been exposed to the environment as much as the rails and not had a good grease packing first, most likely need replacing (or will in the near future).

Strongly suggest going to a more modern smaller vacuum pump or even going over to a venturi system as that can get you the pressure levels you are going to need. Also look at getting some MDF (19mm will work) as a working bed. The level of vacuum you need to run something like that will pull right through MDF. Does it come with zones on the bed for the vacuum? If not you will want to get gasket material and set up some zones to save on force and power.

Looks like you did good on the purchase from the struture. The drivers leave a bit of a question or two for me and finding out what type of stepper motors it is using will also let you know what realistic feed rates will be and if you need to be looking at moving to servo's or to the hybrid close loop steppers.

Good luck and well done hopefully everything can be brought up to full functioning quickly.

Michael