If these are your first goats or sheep your tags (ordered from Daltons in any colour other than red or black) will start with your herd number and then the second number starts from 00001. You probably have to order a minimum number of tags, so they will last you a few years. Your registration number will not be on the tags, and yes only the female needs to be registered - cheaper to do before they are 6 months old. I usually wait until they are at least 4 - 6 weeks old, just to make sure they are viable etc. Castrated boys cannot be registered, entire male kids yes - but more expensive and only useful if they are to be used for breeding. I assume any boys will be castrated? But wether kids will need tagged to go to abattoir, in theory only a single slaughter tag if younger than 1 yo. I have always just double tagged the boys too, it's not that much more expensive for double tags vs single tags if you only have a few goats. But then mine are often GG boys and I leave them until oder than 1yo.
You don't need to tag until the kids are 6 months old or when they leave the holding, whichever is sooner. Vet visit for disbudding doesn't count.