OK so I'm not going to try to influence you but I'll share my situation and perspective for information and you can do with it what you will.
I have Bagots and chose to go down the SRUC accreditation scheme route because I believe in the long term health of my stock, anything I breed and the breed as a whole and wanted to ensure I was setting myself up for success rather than heartbreak. I'm not commercial but I am doing some conservation breeding and therefore I've kept what I've bred to date. I run males and females. I tested for CAE and Johnes pre purchase and have tested for those plus EAE since. I enforce biosecurity which means my stock doesn't come into direct contact with stock from another premises, including at shows (very few will accept accredited goats anyway). I put their health ahead of showing and if I'm not happy with the show biosecurity, we don't unload, we come home. The scheme is restrictive in order to protect the animals health and, subject to meeting the rules and remaining negative on results, testing moves from annual to triennial over time with only a proportion of stock tested (based on trip size). If you want to check out those in the accreditation scheme for "availability" etc you can use this link and sort by breed.
http://www.psghs.co.uk Not all those with accredited animals will "stud" their males due to the increased risk of biosecurity breakdown from incoming stock, even those with a similar status.
The British Goat Society has set up a competing scheme based on the same tests but with lower biosecurity. Whilst it is cheaper initially, the whole trip gets tested annually in perpetuity. You need to be a member of BGS to join that scheme and it's probably the dominant scheme amongst dairy goat keepers, particularly those who show.
Commercial dairies tend not to test, with many having "positive" stock on their premises and therefore those who sell to private keepers (for example downsizing or closing the dairy) can be a significant source of infection to keepers who fail to ask the right questions or perform the tests pre and post sale to ensure they're buying healthy stock. I understand from others this has been a significant issue over the past couple of years as there's no requirement to disclose known issues with stock health on sale and many "new" keepers don't know what to ask in advance of buying stock. Some of these animals come with excellent pedigrees and people think they're buying a bargain.
Schemes aside, if you're just looking for a test certificate for service, then your vet can do the bloods and send them away for testing which gives you the certificate you need (subject to negative result).
In terms of ages of breeding does. My matriarch kidded successfully for the first time aged 5, with another of my girls having her first aged 8 (she went on to produce twins the following year and triplets the year after). I don't have a full history for either of these goats so can't say if they were covered every year and aborted or if they were late being served but neither had problems with not kidding as a 3 year old. I'm aware that others feel this is a problem, particularly in milkers but don't know how much breed influences that. I, personally, wouldn't worry about running a goat an extra year before kidding if I felt it was the right thing for her/me. If you do decide to breed them all, there's nothing to stop you staggering them so that you cover one early in the autumn (say August/September to kid January/February) and another at the tail end (say February/March to kid July August). At least that way you're staggering the milk production by a few months.
I've inferred it's the kids you'll sell on rather than your originals, but another option would be to kid all three then sell one or two of them (the more difficult to milk or those with male kids at foot) and keep one or two with female kids with a view to kidding the kids once they mature. You could try to run through the milking to give you longer production.
If you're looking to breed "pets" then work out what the market is in your area - polled, horned, disbudded; pygmies versus GG types etc. You may find a pygmy cross will be more saleable as a pet than a GG type based purely on size... equally if you're looking at meat then you may want to cross with a boer to push the growth rate of the kid and give a bigger carcase.
Good luck, whatever you decide.