The oil filter part # keeps changing, so I really don't know it, but they're pretty easy to come by. Try to stick to a fleace filter instead of a paper one.
I believe the air filter part # is 112 094 06 04. I just happen to have a pair sitting in my living room that I was thinking about selling.
Stick to full synthetic, along the lines of 0w-40 or 5w-50.
716.6 something something
'03 is when they finally started getting the 203's right. Remember, "started to". Alot of the problems that the '01's and '02's are fixed. But many of the early '03's still share similar problems. footwell flap levers for the AAC system break. Radiators leak coolant into the trans cooler, not in your case though, since it's a manual. Front swaybar bushings squeak. Front swaybar endlinks click. Front torque strut bushings crack and leak. Instrument cluster display starts fading. Numerous updated part #'s are available for the front and rear SAM's. Tail lights burn out early. License plate lights burn out early. Front turn signal socket contacts burn up. All these things I just mention pretty much have a bulletin for them. And pretty much all of them have updated, improved part #'s to fix them.
The 6-speed is the way to go, though. It's actually quite durable. If you drive it right, the clutch should last a long time. And it also gets rid of the horrible throttle lag that plagues the automatic C240's, so it actually has decent pick-up.