There are as many opinions on good diff oil combinations as there are 8th buggy racers. I know people that run 30,000 F, 10,000 C, and grease in the rear, while other folks will run 5,000 F, 3,000 C, and 1,000 R in the same car. I've even seen heavy shock oil used so it's one of those things you will have to experiment with. A good beginners oil setup is 5,000 F, 3,000 C, and 1,000 R. This will give most japanese buggies a very nuteral feel, but will cost you in both off power steering and straight line acceleration. Another very popular combination in Japanese buggies is 7,000 F, 5,000 C, and 3,000 R. With this setup your buggy will corner better off power and will also hole shot better, but it will also step out faster. The idea is to get you car to follow the front wheels so whatever oil you use in the center, use a heavier oil in the front and a lighter oil in the rear.
As for sway bars, if you are running a mild engine they won't do you much good front or rear. If on the other hand you are unning something hot, putting a sway bar on the rear will give you more steering. The general rule of thumb for sway bars is whichever end of your car needs more steering, put a bar on the opposite end.