saddle and bridle- brown leather preferably but black is fine aswell, straight cut(ish) saddle and a plain, flat cavesson bridle with a snaffle/pelham/double bit. no numnah or a close cut, plain numnah that you cant see, matched to saddle.
if you are showing him long and flowing (not hogged) then just leave him as he is, maybe level the mane and tail up a bit (dont cut the tail straight across bottom, leave it shaped) make sure he has a couple of good baths to get him nice and white.
you should wear a tweed jacket, beige/canary jods (just not white or black) and a shirt and tie (not a stock) and long boots (or short will be ok if you dont want to buy more)
Inhand, use your ridden bridle with reins taken over the head and you wear dark coloured trousers because he has light coloured legs along with your tweed jacket or waistcoat if it is hot. wear jodpher boots (or any sort of shoe) that are clean and tidy and comfortable to run in, even trainers.
think this is most things
good luck, he his smashing