First and foremost, get some behind-the-counter experience in an existing shop. It's a tough business, a sometimes unpleasant business, and you want to be aware of how gruelling it can be before you strap yourself to the "weekly wheel". Many comic shops welcome unpaid/paid in product volunteers/interns. Just ask.
Handicap: The lack of punctuation or capital letters in your post indicate that some sort of dysfunction may lie in this area. If this is the case, be advised that you must be very careful in dealing with Diamond. Very careful. I can't emphasise this enough.
If you make any kind of mistake in ordering, chances are Diamond will not or cannot correct it. If you order 10 statues instead of 1, you will get ten. You might be able to plead for mercy once. Might. Once. Diamond is very unforgiving of mistakes that are not their own. So if your handicap is in this area, check all correspondance to Diamond very carefully.
Otherwise, well there's lots of us with handicaps. We can't say that a handicap "shouldn't be a problem", because it always is, but we've learned to adjust around them, yes? Comic retailing is no different from any other endeavour- I've known dyslexics, parapelegics, stroke victims, amputees and so on that have been successful in this business- it just requires the "usual" extra effort...