Chip colours are not decoration. A dealer reads a stack from across the table by colour alone, and a set where the 5 and the 500 look alike will cost somebody a pot.
Pick a scheme and see it drawn. The casino convention is offered as the default because it is what most players already read fluently.
White, red, green, black, purple. It is the order used on almost every casino floor in the world, and the reason to follow it is that half your table already knows it without being told. A set that invents its own order has to be explained every time somebody new sits down.
Under a bright light, red and orange chips at a distance are the same chip. Pick values that differ in lightness as well as hue, and the stack stays readable when somebody has pushed it into the middle.
Whatever scheme you pick, you will run out of the smallest chip first, because that is the one the blinds are paid in. Nobody has ever finished a game wishing they had bought fewer.
Green, on virtually every casino floor. White is 1, red 5, green 25, black 100, purple 500.
Three is enough for a home game, four is comfortable, and six only earns its place at deep stacks.
No. Blank chips let you assign values to colours as you like, which suits a group that plays several different stakes.