Wow! That's some heavy set of questions.
I don't know anything about that surface grinder, but I do have an oldie that I bought 10 years ago so I know what you are going through.
Where to start?----
I don't think I'd ever buy a surface grinder before seeing it run.
Hydraulic: My old Gallmeyer and Livingston 8" X 20" surface gronder is hydraulic. What the means is that the X (left to right traverse) table movement is driven by a hydraulic system pushing a cylinder that is coupled to the table. They call this a "trombone" This means that, in addition to the the spindle drive, you have to know whether that hydraulic system is in working order or not. On my grinder, there's no manual table drive, so if the hydraulics don't work, the thing is just so much junk. Some hydraulic surface grinders DO have manual drives, but at least in larger sizes, you'll get a huge set of biceps from doing it that way.
The spindle is the big thing. I'd guess that worn spindle bearing as a major reason that surface grinders are taken out of service. A new set of bearings can easily cost $600 or a lot more and they require special treatment to replace. ---Not that it can't be done. My brother, who spent a lot of his career at Gardner Denver, says that if you can "hear" the bearings, they are bad. I CAN "hear" the bearings on my 1935 machine, but I can hold 0.001 okay. But a good surface grinder should hold 0.0001.
Weight: Surface grinder can weigh a LOT. Mine weighs 3500 pounds. Think about that.
Power: Check to see that you will be able to power it at your house. These machines are often 3 phase. Since the machine you are thinking about is hydraulic, you won't want to be changing speeds, ala VFD, so think rotary phase converter. And remember, VFD's can be hard on motor windings not designed for the voltage transients a VFD can produce.
Spindle size and wheel size: Make sure you know the spindle diameter and the size of wheel that you potential candidate uses. Mine has a (now) obsolete 2" diameter spindle, I have plenty of wheels for it, and I can get the wheel vendor to bore out wheels to fit, but it's no fun to go through the process. I have made up an adapter so I can use
3" bore wheels and I have a lifetime supply. I don't change wheels very often, so it's not an issue any more.
Maximum height that the spindle with wheel will allow to be attached to the table; Maybe not an issue for most, but I needed a lot of room, so I could grind blacksmith anvils.
Coolant: NEVER try to run dry unless you have a GREAT dust collector. I ground my first anvil dry and it took me 2 weeks to clean the shop. I'd definitely choose a machine that has a coolant system or I'd (as I did) make one.
Accuracy and size: Spend some time thinking about what you want the thing for. Then buy accordingly.
Chuck: Does it have a magnetic chuck? You WILL most likely need one sooner or later. Lot's of old surface grinders will have electric powered magnetic chucks. Be suspicious of them unless you know for sure that they work and are electrically safe.
Parts/Manuals: I needed one small part for my grinder to get it to feed automatically in the Y direction (in and out). The company wanted $650 for it. I made it myself, but it was quite time consuming. As soon as I got my machine, I contacted the company and they sold me a manual for $75. It was worth it. If I were you, I'd check on manuals and parts availability BEFORE I laid down the cash.
Price: Note that you can buy a brand new Chinese 6 X 12 manual grinder for $1000. Also note that a new high quality 6 X 18 can go for $10,000. I bought mine from a dealer in the Mpls MN area, paid $750 for it and thought I got a good deal. See what used surface grinders are going for on Ebay.
It's little like getting married; once you've got it installed, it's going to be around for a while.
Good luck, Pete Stanaitis