|I'll answer your show grooming post later on when I have more time, but regarding grooming powder: I believe that the term "grooming powder" is most often used to refer to the color enhancers used by cat show exhibitors--sparkly white, reds and browns, black. Many people with longhaired cats will use dry shampoo (the powder kind) to mop up any kind of residual grease, like stud tail or clumpy fur on the bib, behind the ears, or under the armpits, or to give fullness to the tail. Some use cornstarch or baby powder for the same reason, although I suspect that baby powder may not be designed for being licked by cats.
Whether used to enhance color, mop up grease, or give added fluffiness, grooming powders should be used with care, especially right before a show. They're not a violation of show rules, but it's bad form if your cat sheds powder on the judging stand, or if the powder makes the cat sneeze (everyone will think your cat has a URI). Persian exhibitors are the ones who most commonly go for grooming powders--they come with bags and bags of grooming supplies, including human makeup (for around the face and eyes), and will sometimes rent a separate grooming space. There are, apparently, some differences in grooming techniques used by Persian owners and Maine Coon owners; I'm not sure about Norwegian Forest Cats. Some people who are showing a cat for an extended period of time (for a whole season, or at least until it Grands), will even go through a special grooming routine even in the days or weeks between shows, not just during the pre-show grooming session, which is one time when a powder shampoo can come in handy. I don't do that myself, but it all depends on the exhibitor, the breed, and that particular cat (every cat, I've found, even siblings, has a unique coat with unique needs).
I've never used a color enhancing powder, although I did buy a bottle at the last show--red, to brighten up my red tabbies and the red areas in my torties and brown tabbies. I also use a red color enhancer shampoo for the same reason, and a whitener for the white areas on my "and white" cats. Obviously, if you use a color enhancer, whether powder or shampoo, don't get it on the white areas! Maine Coons tend to be "greasy" cats, which is why degreasing is so important. Most of my degreasing occurs during the shampoo routine, but if I see a greasy-looking area (shiny or with clumpy fur) at a show, I'll run some dry shampoo through it. My line of Maine Coons have only so-so tails, and I use a spray texturizer and a dry shampoo (not simultaneously) to give their tails more volume, although I'm not really sure how effective that is. Maine Coons are supposed to be "shaggy but silky," so "puffiness" is not as important as it is with Persians; I'm not sure about Norwegian Forest Cats. As I wrote above, color enhancement and degreasing can be part of the shampoo routine; most of your degreasing (which is important for NFCs as well as Maine Coons) will occur during the shampooing stage, with powder used mostly for touchups and in the case of "accidents" (going potty, vomiting up hairballs, and the like).
As for brands, Jerob House of Anju is a brand I see a lot in Japan, but there are others. Cat shows always have vendors who sell things like grooming powder, and you can also check the Internet, or ask other exhibitors (at shows or on show cat websites) for advice or recommendations. I wonder if dog products can be used on cats--there seem to be a lot of them out there, and they're guaranteed to be non-toxic, at least, although they may be too harsh for a cat. I don't know what the situation is in the U.S., but in Japan, you can't find commercial grooming products at pet stores, only at shows or over the Internet.
I'll answer your show grooming question later when I have time. I've basically taught myself how to groom my cats for shows, and I must be good at it, because judges often go out of their way to praise my grooming, and other exhibitors will often ask me if my own breeder taught me. Nope, I just looked stuff up on the Internet and learned some hints from other groomers. And I learn as I go along. One thing I learned this season, when I had two cats make Regional Winner (Harvard and Lowell), is that there can be a big difference, as I wrote above, between the grooming needs of individual cats. Harvard and Lowell are littermates; both are big cats with rather scanty tails. Lowell, the brown tabby and white, is an extremely greasy cat who needs serious degreasing on a regular basis. When I used the same grooming routine on Harvard, who is less greasy, his fur got somewhat dry and brittle.