1. Trans has about had it at 270k, just run it until it fails.
2. 300-400 miles on a quart is large consumption. Do you foul out plugs? The gasket likes to leak from the back by the number six cylinder, the front cover, and also the side like my car. Also the front main seep with age. You may be up for another gasket at this mileage.
3. Just pick up some three and four way connectors plus some 3.5mm? ID tubing to replace the vac stuff. The breather and PCV hoses are self explanatory as are the idle control valve ones. May want to reseal the injectors (o-rings) and consider the AFM boot if very stiff.
4. The shocks/struts on there are long dead. Rears just bolt in, fronts have upper mounts and boots I would replace while in there last I can recall.
5. Ign components on the M103 do not last long, at least the cap/rotor/plugs in my experience.
6. Yikes on the diff. I would drain and refill... run for a while, then service again.
Otherwise do as the others pointed out and enjoy the car.
Oh, go hit the dealer and attain a high mileage badge.