1) There is a service indicator when you start the car. It tells you the number of miles until the oil change. When reset (look online to learn how to reset when you do an oil change) it starts at 15,525 miles, but the actual miles will depend on how much gas you burn. More gas, less miles. Some people change the oil at mid-point of the countdown (7750 miles).
There is also a requirement to change the oil every 12 months if you do not reach the mileage point. You do NOT reset the oil service indicator when doing this oil change, unless you are very close to hitting the mileage point (about 1 month of normal driving).
2) The ONLY oil that is approved with this engine is Castrol TWS or RS 10W-60. It is not a common oil. You can get from a dealer or some online shops. If you join the BMW CCA most dealers give you a nic discount, making the oil not too bad, but it isn't cheap. Since you are out of warranty, you can use whatever oil you want, but I use the Castrol TWS.
3) Only premium gas. I only buy from branded stations (Sheel, Rexaco, Exxon, BP, Sunoco), not off brand of independent stations. The car will actually produe more power using fuel up to about 96 AKI. This is about a 50/50 mix of pum premium and UNLEADED race gas. You can find unleaded race gas at some Sunoco stations.
'95 Alpine M3 LTW
'00 Dakar M Roadster
'02 Topaz M3
Red/White SRF #4 (Chassis 561)