Oldhorselady is right, trailering is an issue. My draft is 19hh and more than 90" long chest to tail. He does not fit in a "regular" trailer. Also, you have to make sure that you have a bigger truck with a large tow capacity because weight of horse plus trailer is a big load.
As far as tack, I bought my saddle, a dressage saddle from Ebay and my bridle from a draft horse supply shop in NH, and the bit a 7" snaffle I bought at my local grain store. I did have to special order my dressage girth as I couldn't find one long enough at my usual shopping places. My halters, I have rope, which I made, and a "regular" which I bought at my local grain store, though it really doesn't fit his Percheron moose head. I do like longer lead ropes, 12', as the ones you mostly find are just too short and don't give you enough room when working with a big horse.
Draftguy is also correct in that working with a big horse can be a bit intimidating at first, just because of the size, you QUICKLY get over that, until they do step on your feet. :) Though I ride mine everyday, and once you get over the fact that your head is 10' in the air, you are fine!
My guy is the biggest in the field, he lives with 2 Belgian mares, both 1800+ pounds and 16-17 hands, but he is LOW MAN in the field. The mares are the bosses, normal. His size does not matter to them at all!
I LOVE my draft, but I don't think that they are for everyone. Though, I will never own anything else now that I have gone draft.