Read the sticky posts at the top of the forum Periodic maintanence manual among others...
To answer some of your questions:
Oil: 5W30, synthetic or regular thats a matter of opinion
ATF: DEXRON III ATF or better
Rear Diff: 75W90 gear oil
Periodic maintanence is no more difficult or easy than any other vehicle. Oil changes are easy. Rear diff fluid change is easy. Look around all your questions have been answered before. Overall Subarus are pretty reliable and durable vehicles, I would not be scared to buy one