17's max, but I think 16's look better, also a 65mm drop is all you should be looking at if you lower it - any more and you look like a tosser.
Kit wise, i thinks it's best if you stick with the traditional Alpina, Hartge, Mtechnik, kits as these look best . i have never liked the zender kits or some of the new stuff out modified for E30's.
As far as rims go, stay as far away from chrome as you can, go for something basic, or get some Alpinas - Alpinas are the sha-nizzle.