Well, if it was me, I'd probably wait to see how the kits look. The idea with culling is to make careful decisions. For instance, will the new kit bucks be better than the sire? I have an unpedigreed American chin doe who is sweet, gentle, kind, and the flat out best momma I've ever had. I kept her first daughter and bred her. She is sweet and gentle, but lost 3 kits out of her first litter of 8, and despite being 2 weeks younger than her mom's litter they are smaller--strike 1. Now she's had a litter of 11. They are tiny. She's feeding them, but I expect to foster half of them on to her mom in a week or so, just to keep them growing. Meanwhile Mom raised 9, and they are fat and sassy and ready for harvest weeks ahead of schedule.
Point is, right now Mom is the keeper. This fall I'll cull the daughter and raise a different girl from the good momma.
Your buck is half your herd, so pick the very best one you can.