What is your goal in regards to feeding seeds or extra grooming?
All rabbits should have regular nail trims, and be brushed or combed out if they are tangled or shedding heavily.
Feeding a rich food like black oil sunflower seeds(boss) would usually used to help a smaller rabbit put on weight, increase milk production, or provide extra calories to help a rabbit stay warm in winter. Pumpkin seeds can be an excellent alternative, if they are readily available in your area.
With all new foods, introduce them sparingly to rabbits over 8 weeks old, and gradually increase the amounts given until they are eating the amount you desire them to have.
I do not recommend introducing anything new before that age.