I raise Nigerian Dwarfs too. I don’t breed my girls until they’re 18 months old. I’ve found they’re mature enough and big enough by then.
There’s a lot of information out there but a lot of it is outdated like Fiaso farm.
The Storey book on raising dairy goats is good. I find most of the best information is right here on TGS.
As far as preparing, before breeding I’d get a fecal to make sure your doe is worm and coccidia free. Trim up her hooves and make sure she’s single teated (in nigies you don’t want extras) make sure she’s got a good body score, not fat, not thin. Check for the big three CAE,CL, Johnies.
I take my girls on dates with the buck. When they’re showing signs of being in heat they go in for 24 hours, then 5 days later they’ll go in again if they’re showing heat signs again.
Wait 17-22 days to see if they’re in heat again if they are, back to the buck. If not, wait 10 days and pull blood for a pregnancy test if you want.
3 months after breeding, another fecal check.
4 th month, final hoof trim before kidding and CDT
4.5 month give calcium gummies and raspberry leaves daily and prep kidding kit.
4.75 months start pulling hair out from excitement And give one cup grain daily
5 months...happy kidding!
Day after kidding, worm if needed And start upping grain for milk production And play with kids