Some of that is going to depend where you are showing and who the judge is. If you are showing at a draft show, than show him like a draft. They are turned out the same as Percherons and Belgians. More common to see long manes so clean it up if it's raggy but leave as much length as you can. A white halter is always appropriate but it can make the head look chunky. Going down to 1 1/4" leather will help. You do see black trimmed with silver halters but make sure it is right for him. Mature horses are supposed to be shown with a chain. His mane should be loose or rolled with flower springs. Forelock braided. Hoofs black. Legs are slightly hairier (trim the long hairs down the back of the leg) but trim the coronet band (clippers going up against the grain) to make his hoof look bigger. Clipping is as extreme as Arabs. Every last hair has to go. (and oiled up) Tail down. When he's lined up next to a big Belgian gelding, he will look like a miniature version of him. You do not wear anything blingy. Color coordinated polos and pants are standard. Do not need a hat. Need a show stick.
If you are showing him in an open show under Quarter Horse judges and you want to place, show him like a quarter horse. If you want to mess with their heads, show him like a draft. Square him up like a QH too.
Under saddle, stick with a more traditional QH turnout both ways. Long mane and tail for western. Control the mane at least for English.