If you only have a couple of nannies, I would not keep an entire billy, but use a stud one. Believe me, the amount of feed and haylage Paddy can get through over the winter, I could have paid a few stud fees!! Remember, if you keep any nanny kids, you will then have to find another billy for them ......so your entire billy would be sitting there doing nothing once he had served your two females. An expensive commodity!!
He would need his own area away from the nannies, and they can be strong, and wreck things when in a strop (or thats just how they are in general) And the smell which we have discussed before.
Use a stud billy the first time and see how things go ......you may decide a billy is not a good idea then. As to horns, well, traditionally you see Billies with big horns, and both mine had them but that was not my choice. Personally, I would prefer de horned goats, its safer for the other goats, and for the humans dealing with them.
Visit someone with a stud billy, and you will get the real picture on what its like. My opinion is keeping intact billies is not for everyone, and you need to be experienced in goat keeping before getting one (not that I am suggesting you are not, its just better to know what you are doing in general before deliving further into it by keeping an entire billy is what I mean!)
I have entire other animals, and its not just goats, they all need very firm handling.