A co-worker is moving and offered to sell me an Estate Heatrola for $100.
It appears to be a good deal because it looks like they typically go for $450.
I don't need a good deal on a big antique though so I'm wondering if they are a good functional heater?

Yes they were good. Don't know what type of coal ( anthracite or bituminous)is available
to you but with anthracite the heat output was high. I had an aunt and uncle who used one
similar to that and the cousin who got the house after they passed is still using it.

Just check the grates inside. If they are in bad shape you may not be able to get new ones.
Around my parts we have a stove dealer (in Tamaqua) who can get obsolete grates but
naturally they aren't cheap and thats if the stove was popular.

As far as burning wood in them I know nothing.

Get the model number and check on-line for parts if you need them. Just Googling the name gives you plenty of good responses on it being a quality heater. We burnt wood in our Warm Marning and King-O-Heat for a lot of years when we first cleared off the lot for the cabin. We now burn coal but I recently got 2 cords of wood from a neighbor cut to fit our stove so we'll be burning more wood this year.

Check with some of the feed/grain stores, they may be able to get coal. When my uncle bought his outside stove he also bought a pallet of bagged coal to use with it from the stove dealer.

Go to nepacrossroads.com and look in their forum on coal heating.
Prepare to learn a lot.

No really, when I started burning coal last year, I found the site and spent days increasing my coal knowledge a hundredfold.

haha, so how about those cliff notes?
He's moving this week so I don't have time to become a coal expert.
Main concerns are... Is coal available and economical? Does it have good energy density? and finally... Do these types of heaters burn wood well or is it a huge pain in the ass to cut
wood into small enough chunks to fit inside it as well as the energy density of wood being too low as to require frequent refills?

Coal has great BTU density, it keeps well, it is pretty cheap- but that might depend where you live.  Yoiu really need to see the condition of the inside of the stove though.  Coal stoves tend to burn out over time depending how they were taken care of etc.  If the grates and interior are all eaten away or warped they can be a pain.  We had 1 or 2 of those stoves when I was a kid, I think there still might be one in my parent's cellar and there was one abandoned in the last apartment I had. For $100 it could be a great deal but there are other stoves out there now that I think are better- particularly when you consider the possible neeed to replace parts.

Can parts be fabricated.
I've got Engineering experience and equipment to work with metal.
Not that I need a another project but it would be an option if the stuff that wears out could have replacements welded back in.

I can get coal for $45/ton, I haul and unload. That's the best I can tell you on coal. My brother is a mine boss, we presently get it for free. If coal isn't available burn wood. How much wood, that depends on your house size and if that was your only heat source, it is my opinion you will burn 2X more wood than coal. We heat our cabin with a Warm Morning 521, no other heat sources. I have a WM 521 sitting in my building ready to use as a back-up if ever needed and a cord of wood. Coal will create more of a mess than wood.