Full time job = 24 hours a day, quite literally. Good breeders sit/sleep/eat with mum and then litter from about a week before she is due until the puppies are several weeks old. They do not go out. They do not leave her and the pups. They have a good knowledge of veterinary basics so they can quickly assess and handle any problems - and know when a vet is needed. They understand genetics and how two rights can sometimes = a wrong.
Good first time breeders find themselves a breeding mentor - someone who has bred for years and has a really good handle on what is happening. That mentor is on hand, full time throughout the first few litters to provide advice and support.
Good breeders also have a really clear idea of what their dog brings to the gene pool - and just being KC registered is not enough. What is so special about your bitch that you think she would produce BETTER puppies than her? What is she missing that you would be looking for in a stud? In GRs that have so many individuals in the gene pool, I would consider it very difficult to have an exceptional individual that can add something
Good breeders will have a second, experience breeding bitch on standby in case their first-time mum rejects the puppies. They do not take risks by breeding with just one, untested individual without a back up plan.
They will also have considered the temperament of the breeding bitch and whether or not she is likely to cope with a litter. They will be using their experience of breeding (or their mentor's) to make that call, not just "pet" knowledge.
Health checks are covered in depth throughout the KC website - start here www.thekennelclub.org.uk/media/451962/breeding_health.pdf
In my humble opinion (and I say this as gently as I can), good breeders don't do it because they fancied having a try and their kids love dogs. Personally, I would not buy a pup from such a set up for all the world. Others will, though.