I started my herd with pure saanens, crossed with Boer.
I now have a variety from pure saanens to 87% Boer (plus 100% billy).
I have had dairy nannies that have been weaned and require regular milking (once or twice a day depending on yield as don't want to leave them full and uncomfortable) but I have also milked nannies that have kept their kids with them. Either when just a single, I would milk the other side every day (or every few days if not requiring as much milk) or separating the kids overnight and milking in the morning and allowing the kids to be with mum through the day. The trickiest part of leaving the kids with mum is that she will naturally wean them somewhere between 6 and 10 months of age, so if you want to keep getting milk, you have to increase what you take - if the kids take less, they will start to dry up without stimulating more milk production by milking them. Some people prefer to remove the kids and bottle feed from a very early age to keep a controlled milk yield, but this does require regular milking all the way through.
One of my best goats has been a 50% Boer, who raised twins in her first year, and gave some milk for the house, and triplets the next two years. She had a stillborn kid this year, but her other nanny kid is doing well.
The Boer crosses do produce a good carcase, and as the dairy/dairy crosses produce a lot of milk, they certainly grow rapidly while still on milk.
If you wanted to talk about it further you could send me a message, or I'd be happy to show you my goats, I will have some for sale. At the moment they would be with kids at foot, or could sell weaned off preferred.