-It's hard to answer to the first question because we don't know your regular mechanic's skills and tooling on BMW. I suggest to find a BMW specialty shop in your area. I can help you with this. Their prices will be somewhere between the dealer's and your regular mechanic's price, but least they know what they are doing and have the special tools necessary for any further repairs. Although a pinion seal and belt replacement are not a big deal, the best what you can do for your car is to have a good relationship with a honest BMW specialty shop.
At 100K the following services are due :
- ATF (since you have a manual transmission it won't apply to yours, however you planned to replace the fluid in the MT also.) The correct MTF is : MTF LT2 if you can't obtain this, you can use the MTF LT1, which is the older version.
- Spark Plugs (due at every 100K)
- Oxygen Sensors
- Brake Fluid / every 2 years
- Coolant (only the original BMW blue coolant) every 4 years
It doesn't have to be done by the dealer, I'd take it to a BMW specialty shop.
do you know if the 90K service was done?
The life of the clutch is greatly depends on the driving style, There is no regular replacement interval. Replace it only if it slips - among the release bearing, pressure plate, pilot bearing and rear main seal, the DM Flywheel might also has to be replaced.
I like Mobil1 synthetic, they have a 0W40 designed for European cars, approved by BMW, MB, VW, Porsche, etc.. and available in most part stores. AmsOil is also a great oil, but not as well distributed.
The OE oil is made by Castrol - which I'd never use in my car.
I'd change it somewhere between 5 to 7500 miles, based on driving circumstances.
Lots of stop and go city driving - especially in hot temperature, sporty driving style - I'd go with the 5K interval. More regular driving on highways - go with 7500.
The oil filter quality is also important. Use Mann, Hengst, they are the OE manufacturers. Did you remove the oil filler cap and look inside? Do you see any brownish deposit and sludge? I hope it's clean.
Around this time you can expect some suspension issues, like struts, control arm bushings, ball joints. Get the front CV boots inspected (keep an eye on those at every oil change, they are prone to fail and cheaper to replace the boot only, than the whole axle!) The PCV (breather components) system might need to be replaced soon. It includes the breather-oil separator valve and 4 hoses.
Rotate the tires at every oil change also. Make sure the shop is using a torque stick or torque wrench on the lugs.
I'd also suggest to call the dealer with the VIN and ask if there is any pending safety recall on yours. They are free repairs.
Enjoy your car for many trouble and accident free mileage.