I don't know many modern Subarus that can pull down 30+ mpg, but most non-turbo models can manage ~28 on the freeway (and ~25 in town.)
If space is an issue, look at the Forester. The Forester is a tall Impreza wagon, built on the same chassis.
Maintenance has it own quirks, but not really that much worse than anything else. The first time I did my spark plugs in my 2000 Impreza, it took me about an hour and i took out the battery and the intake snorkel. Reaching the plugs on the H4 was not an issue, but you will need a u-joint and at least one extension. The flat motor layout is really pretty nice - except for the heads themselves, everything is just laid out right on top.
Pretty close to what you describe - it seems like everything I do under the hood is either with a 10 or 14mm socket. Get a full set of metric, and you should be set.
I haven't heard of any major "known issues" with the non-turbo models since the 1998 DOHC motor. They've done a fantastic job keeping an eye towards reliability. If you keep it tuned to factory specs, the car should behave well for a long time. IF anything, keep an eye on your alignment. If you get out of alignment, the AWD will eat your tires for breakfast.
Hope this helps!
