I use peppers for mead a lot. Usual drill: throw them after bubbling slows down or the smell will bubble away.

A couple of good, ripe habaneros is good for 5L. Don’t use scorpions, they add sting but no other flavor, while habaneros are quite flavorful.

Capsaicin does not have any notable effect on yeast, it’s neurotoxin, after all.