On what to cut, the principle is consistent across most approaches: cut the volume, keep some of the intensity.
Dropping mileage substantially is the whole point, that is what allows the recovery. But cutting the fast running entirely tends to leave people feeling flat and sluggish, and it is likely part of why your goal pace effort felt wrong. Short bouts at race pace or a little quicker, with plenty of recovery, keep you feeling sharp without adding meaningful fatigue.
A rough shape that works for a lot of people:
- Volume down significantly across the taper, with the biggest cut in the last week
- Keep the frequency, the same number of runs, just much shorter. Stopping running for days is what makes people feel worst
- Keep one short quality session in each of the first two taper weeks, and something very light and brief in race week
- The last few days: short and easy only
On length: two to three weeks is the usual range for a marathon, and shorter distances need less. Three weeks suits high-volume training; two suits most people running moderate mileage. One week is generally too short for a marathon.
What matters more than the exact plan is not adding anything. The taper is subtractive.