I do not wish to squash your enthusiasm in any way, but I have found it to be the rare case where the rotors are in good enough condition to just replace the pads.
In addition, grinding the rotors is sometimes possible, but requires an extra trip to some sort of machine shop, and the ground rotors may are more prone to warpage.
Considering new OEM aftermarket rotors are typically $35-40 each, I have taken to just replacing them at the same time as the pads. The money you save by doing it yourself makes the $80 relatively insignificant.

That said, replacing (front) rotors on a 300E is a snap!
1) Remove the 2 big bolts that secure the caliper to the steering knuckle (19mm head,92Ft-lbs torque). Remove the caliper. Do not let it hang from its hose. Wire it up, or set it on something (I use a milk crate-just the right height and size).
2) Remove the set-screw that holds the rotor in place (6MM hex key). Pull Rotor, replace rotor. Replace set-screw.
3) Replace brake pads as described in other post.

Extra credit projects for best results:
1) Apply anti-squeel paste to back of pads.
2) After cleaning with solvent and sandpaper as needed, apply a very thin coat of moly grease to the caliper surfaces that the brake pads slide on. Do not get grease on wearing surface or disk. Moly grease is often sold as "brake grease" in little tubes at the parts store.
3) Apply a silicone grease to the 2 pins (that go into the rubber boots). Most parts stores carry this stuff these days.
4) Bleed the calipers until the brake fluid runs clear. Pushing the calipers back in often forces the scummy fluid that has settled in the caliper (the lowest point in the system) up into the resevoir and the rest of the system. Ideally, you would bleed the calipers before pushing the pistons in. Brake fluid should be renewed annually anyways, so odds are that it is overdue when the pads fail.
5) Inspect the rubber hoses. Do not mess around with these- if they are cracked or have bulges, replace them. I replaced mine recently for just $8 each.
6) Remove, and clean the ABS sensor with brake solvent. It is magnetic, and accumulates rust filings on it over time.

300E brakes are very easy to service, but braking is serious business. This is a place where a little extra attention goes a long way...

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1986 300E 5-Speed 240k mi.