I have one proven buck...6 mos old, and 6 does...two at 6 mos, one 1 year old that has never been freshened, 1 one year old first freshener, and 2 two yr old second fresheners.
I cannot keep the buck in his pen...he slips every fencing option I've tried...seems to not even feel the electric...
Up until three days ago I wasn't worried as I saw nothing to indicate he was in rut or that the does were in heat...but in the last couple of days he's beginning to act...well...weird, and I think he's now in rut, and the does have become far more active. I see nothing that looks like what I've read as far as vulva appearance or color, but they are a LOT more active than before, a LOT more skittish, and a LOT more inclined to "play" fight (head butting, etc) than before the last few days.
I'm not sure if weather in your area makes it different than where I've kept goats so keep that in mind. I've raised all my kids on goat's milk, here in Ca. and in South Africa. Remember when talking generaliztions you can be within a month or two.
Nannys can breed at (remember "about") 8 months. They carry their kid/kids 5 months. After she's stopped giving her babies milk, she can be bred in about 2 months. If she's still being milked or suckling she can be receptive even 2-3 months after kidding as well. If that happens you'll know because she will start drying up earlier than normal. With meat goats we could get two three "harvests" every two years. With milk goats it's better for them to breed them every year at the same time, but I know what you mean about keeping them apart.
I've noticed that Boer goats are becoming popular here. What we did was to breed a boer goat male with a Saanen or Alpine nanny, and we'd get the milk from her for 9-10 months. The male offspring we ate, the females we bred back to meat goats, as the extra milk from the hybrid nanny make her kids grow up fast.
When they are all the way in heat they will do it all day long and all night, at least thats what mine did. It was kind of hard to miss. They might be about to go into heat or something. Sometimes my buck gets more interested for what seems like no reason at all. But when the does are in heat for sure, look out for the love machine.
You can also "tell" when a goat is pregnant by: if they don't cycle into heat again 2 weeks after they were breed, then they must be pregnant. I'm sure theres a more scientific/reliable approach. My goats bred twice before they got pregnant. My buck was pretty young last year when I bought him. It was funny seeing him with my fully grown does. He fought tooth and nail out of the truck but as soon as he got to the fence gate, look out!