Actually if you read through this section of the forum you will find all answers to the questions you asked. A lot of people ask this question.
Here are some things to get you started:
Gentle giants are made not born.
They do not usually eat more than a normal size horse.
They can do just about any of the disciplines out there.
Ground work is the key to establishing a good foundation.
Farriers can be difficult to find and harder to keep.
For the bigger guys trailers can be tough to get.
Don't buy a permanent saddle until after they turn 6 (they are still doing a lot of growing).
Get established with a vet right away. Better to do so now when you do not need one than in an emergency! A vet can tell you what kind of things are lacking in your area as far as nutrients for your horse (in our area its selenium).
Good hay, some sort of fat (it's recommended drafts be on a high fat NO sweet feed diet - corn oil is what I use but there are other options), a block of salt and plenty of fresh water should be all they need.
There is a great book you can get on Amazon
called Draft Owners. Get this book. It is the draft horse bible.
Scratches are usually associated more with a lot of feathers. There are treatments for scratches but they can be really hard to get rid of. I have a Percheron and he's go no feathers so, it hasn't been a problem for us.
Like I said, read through the posts in this section because you'll find a lot of great information.