My speckled Sussex managed to hatch 16 chicks. I think the number depends on the hen, some are better than others.In my experience over about 14 eventhough the hen can cover them it's easier for one or 2 to pop out and not be totally covered and with the hen constantly turning them it could be multiple eggs one at a time not getting under her as they should and possibly affecting your hatch rate. My dedicated broody hens get up to 12 and have consistent 100% hatch rates.
Although you're talking fluffy full size hen so prolly 35 lol