One thing is for sure, parts are not scarce, only the rare ones are, but they've always been like that
Welcome to the forum. I've got an L series that I've had for about 6 years now that has undergone a few changes from the stock setup. Love it and it treats me well if I treat it well - that really goes for anything though.
The thing to look out for is rust around the windscreen. While not entirely a deal breaker its something to be aware of. You can find units around that do not have rust around the windscreen.
The DL is the basic setup. Usually comes with AC but not always. It will be a carbie engine, interior will have vinyl flooring and the usual plastic interior pieces. The dash is a basic layout with speedo, temp and fuel gauges + your warning lights.
The GL is pretty much the same but has carpet instead of vinyl + the door trims have a little carpet on the lower edges. The dash is a 4 guage unit and in my opinion is the better layout over the DL's. It has the speedo and tacho mirroring eachother on the dash with the fuel and temp gauges on opposite sides of the instrument cluster. Look neat. The other difference is that the GL has air ducts to the foot area of the rear passengers.
In terms of the wagons, you'll typically get the DL which is most common and there's also the touring wagons that are basically like the GL but with power windows and mirrors.
You might find power mirrors on a DL depending on what pack it was built as. A sports wagon typically came with white 8 spoke star 13 inch steel rims (sunraisers), tow bar, and a wrap over roo bar (some call it a bullbar). Its basically a dressed up DL with some sort of great stickering down the side of it too. There are loads of different stickers out there too.
The touring wagon also has a higher roof line after the front seats...
Mechanically these little subarus are basically all the same, there's a few differences that can be worked around though, most relate to the difference between the EFI (MPFI - multi point fuel injection) touring wagons and the carbie ones.
Hope this is a help.
Cheers
Bennie