I have ridden purebred percherons and they were LOVELY, and personally own a belgian/QH cross. My belgian cross is just a joy to be around. It took her a few years to 'smooth' out, but she has a nice trot I can sit VERY easily to, unless she's being 'funny' she can REALLY rough it up! lol. If someone gets on her and tries to trot her and they do it 'wrong' she'll about bounce them out of the saddle! lol
In my personal experience I found that they tend to also lean on the bit a little, though I'm sure with proper training you could teach them not to. A percheron I used to own I gave to a woman who now uses him to pull carts down town, to weddings, he runs barrels for fun, trail rides, jumps, and shows in english classes. However, I would suggest a cross if you're looking to get into dressage simply because their bulk doesn't make them 'look' as good at that as some of the lighter breeds.
Also, be prepared for the cost of farrier. Even if all you do is trims, it can get VERY expensive since the farriers I've dealt with charge more because of their size, and thus, the extra work to go into them. You'll need to watch out for flaring and 'pancake' feet if you get a very large one as well.
On feeding...It totally depends on the horse. The percheron I owned ate me out of house and home (which is why he has a new owner now) but my beglian cross eats as much as the quarab I just sold and stays plump.
It's best to have at least 3-5 acres for 'roaming' as well as I have noticed that drafts seem to get bored VERY easily in smaller pastures.
And, just like the others said, cost of tack will be more expensive as well.
Also, don't listen to people who tell you that draft horses are 'stupid' because they're slow. The thing I have learned and LOVE about the draft breeds is, while it might take just a little extra time train them, you only have to train them once. When I got my percheron back from the trainers I was injured at the time and it took me SIX months to get back in his saddle! He was only 4 and only had 2 months training. He was considered 'green' and you should never really let a green horse 'sit around' after it's trained....sure enough, 6 months later I'm feeling better and not 'as' scared (it was a horse accident where I broke my back, so I had lost alot of confidence as well) and that horse acted like he was a seasoned pro! I HATED having to get rid of him, but it was the best for him due to weight issues and the fact that I didn't keep him 'active' enough.
Remember that while Drafts come off as lazy, they were bred to be WORK animals and some have a much higher 'working' drive than others.