Mmmmh.. how long is a piece if string...
So this is my personal opinion.
I have 10 female goats - 3 last years kids and 7 adults. 5 of them are in kid, two running through to provide milk for us in the winter. I do not keep a billy. I am considering keeping a GG male of my older GG girl intact this year if she kids sccessfully, BUT only because she was AI-ed with the last (but one) straw of this particular male and it is a linebreeding. I will not keep (for my own use) any BT males I may have (entire that is, they will be castrated and reared for meat). Even though I think they would make good boys for anyone interested in getting their milk production up a bit. I travel about 250 miles round trip to get my BT's mated... I am mad (I know).
I think with only three females you would be better off selecting a nearby pedigree home (with maybe two different males) , agree what days would be suitable for you to bring your girls, count back 14 days and sponge. Take sponge out on day 12, and they will be in season on day 14. If you are a bit unsure about sponging, your vet will do it. If you are a bit early in the season a PMSG injection will make sure that they definitely come into season, but PMSG costs 40quid a bottle and it stays fresh only a short time, so you would need to get a whole one for your 3 girls.
If you keepp a male all year round and are milking the females, he would have to be kept quite separate form them, so would need a friend of his own (castrated best). Feed costs throughout the year not too high, but coming up to breeding season he would need some protein etc to build him up. He will stink the place down - if you have the general public about regulalrly that may be a serious problem. He will need STRONG housing, and preferably some grazing he can go out on too. If you were to offer his services it would be best if you had a separate area approved by AH to make sure you don't enter into standstill every time there are some girls coming, especially if they only come for the day.
If you take in visiting goats you boy would still need CAE testing, ideally your nannies will too, as you would stand a better chance of selling offspring from CAE negative goats. For example if I were to buy in a goat I would insist on a vaild CAE certificate.
Unless your girls are BGS registered and you are keen on breeding pure, ANY good male (with some milk figures behind him) will give you kids that should be good milkers in due course, but of course any male kid would realistically only be good for curry (and very good the curry is too!).
Again that is only my personal way of looking at it, others may disagree.