Hi - yes maybe to the main section, but rather than repost, and I think rather than having people writing long lists of what to look for in a breeder and reinvent the wheel here
, why not check the many puppy buyer links we already have (box in the right hand column on the main page) that all go into this topic in great detail? The first link is a guide we offer right on this site then there are a number of additional relevant links that answer exactly this question. Maybe read through those then come back with any specific resulting questions? As they will answer all that you have asked above.
Showing is perhaps becoming less of a must-have, as there are a lot of show breeders who do little testing and don't fully, or at all, follow the two main, proven breeding protocols (for SM and MVD). In general nearly all the health focused responsible breeders also show BUT there are exceptions including one of the most health focused breeders I know. Anyone who does NOT show needs to be investigated carefully -- but then so do show breeders, who can be as deceptive as the puppy farmers and backyard breeders and online puppy outlets (and I am talking well known breeders here, internationally) -- any buyer really needs to ask lots of questions and ask for actual certificates and discuss health in detail with any prospective breeders. We have heard here of breeders who offered certs that had been whited out and altered to be used for a different dog than was originally tested too, so deception comes in all forms.
There is no difference in the colours (speaking as someone who has owned three of the four, and worked with hundreds of rescue cavaliers of all colours, with lots of cavalier-owning friends) -- it is just a cosmetic aspect to the same breed and it is possible for a single litter to have all four colours (and every cavalier will have in its genetic history, dogs of probably all four colours) so parent personalities, the throw of genes in shaping the individual dog, and the way a dog is raised will have the most impact on the dog a puppy grows into. The latter two are the most important assuming parents do not have temperament issues. Coat also varies per individual and parents will give some indication of what an offspring may look like. Coats with black in them tend to be more profuse but not necessarily heavier, wavier, etc.
They are generally good with kids but many breeders will not home such a small breed puppy to homes with children under 7 to 10 or so (typical age restrictions). Of course all interactions should always be supervised with kids under 10 with any dog ad especially any puppy, which is far more in need of a safe place and time outs from small kids than vice versa. In the Library section I have lots of good links for information to consider if considering a cavalier in a home with younger kids. Cavaliers are a breed with some prominent and widespread health issues one of which (SM) can produce chronic and sometimes severe pain which means that may be a consideration as well, as kids may not really be compatible with a dog that needs not to be handled or touched.
I have a post entitled 'considering a cavalier' in the Library section that is also worth reading for pros and cons of the breed.