Showing a bird begins before the chick is hatched and well into the actual show phase of the process. Start your chicks with a good balanced feed at 18 to 20 % protein, most poultry feeds will be balanced in the other areas you mentioned. Once the chicks have matured to the point they are four to five months of age they should have the balance of the adult feathering in place and the feed protein percentage can be lowered to 16% as anything over this is in my opinion, overkill. Keep your birds free of internal and external parasites, your local feed dealer will have wormers and sprays or dust for these pesky parasites. Do your best to keep your birds out of direct sunlight as this will damage the feather color by fading darker breeds and yellowing lighter colored breeds. Pen your birds on a good sized pen with plenty of room and grass or keep them in pens with deep pine shavings to keep them clean. Wash your birds 5 to 7 days before the date of the show and then all you will need to do is touch up on show day. I wash with horse shampoo that contains lanolin which adds oils back to the feathers but cleans them well. I always recommend coop training your birds well before the show, put them in pens that simulate the show conditions and have non-poultry people come and tour your birds to get them used to others and all the traffic they will be subjected to at a show, no one likes wild and crazy birds at the show especially the judge, so handle them often and they will respond in kind. Keep you some treats such as small sized soft dog food and toss them treats as you pass by the cages, this will train the birds to come to the front of the cage and show instead of running to the back for cover.
Just remember, showing poultry is not about the poultry but the lifetime friends you will make in this hobby, time spent with friends is fleeting and we should covet such time more valuable than the most precious of metal or stone.
With peace and blessings,