For the BRZ, most maintenance items are pretty easy except for the spark plugs. Subaru service manual includes a 17 page description on how to do it, including raising the engine. However a member here figured how to do it simply by moving a couple of hoses and an ECU:
http://www.ft86club.com/forums/showthread.php?t=88906
Changing differential fluid is as easy as removing the drain plug, draining. Replacing the plug. Then removing the filler plug and filling it back up.
Changing the transmission oil (manual) is not that much more difficult. You do have to remove a skid plate under the car to get to it though. Not that hard to do. You can fill the transmission from the engine bay if you run a hose down to the transmission filler. Only trick to the manual transmission is that it requires a GL-3 or GL-4 rated oil. Don't use GL-5. Motul 300 or Pennzoil Synchromesh works fine.
Air filter is simple. Oil change is super easy. Oil filter is on top of the engine. No mess...
Cabin filter is behind the glove box. No tools needed to replace it either.
You can take most of the car apart with a screwdriver and a butter knife (better to use a plastic body panel tool though).