No your tack can be brown and you can wear black
If you can afford a flashy belt/buckle combo then go that route, if not get a black belt and spend more on the buckle
It will be easier to get a red/black slinky the pastchio so I would got the red/black route.
I wouldnt body clip unless you have done it before and you could blanket him after to keep him warm, your better off just point clipping.
Clip:
Bridle Path
Fetlocks
Trim along hoof/hair line
I would scissor:
Face whiskers-muzzle-surrounding eyes(make them flush with his coat, dont dig into the coat then it will look like he has wholes in his face)
If he has any longer hair under his chin and bottom of muzzle (my horse gets like billy goat kinda longer hairs in the winter under his chin, if your horse gets those too just trim them level with the rest of his hair)
If he has any long hair sticking out of his ears just trim it level with the curve of his ear. Dont worry about the inside