You can always contact the pre sales team of dressilyme.com to ask all your questions. If they made the dress before and took pictures, they probably will send them to you if you ask. Adding changes to the dress is almost always possible. If
they think it will not turn out ok, they will tell you. I also asked for a couple of things they weren't able to do. I think it's better they tell you honestly that they can't make something, so you don't get a dress that's not ok.
Your concerns about the sizing shouldn't be an issue if you let a proffessional seamstress measure you. The dress will never be 100% the same, because Dressilyme makes the dresses from the pictures. If you want the exact same, you should buy the
original. From all the threads on this board with lots of pictures you can decide if you think the dresses are made the right way or cheaply. I think there are a lot of examples on this board that shows the dresses are beautiful! If you want to
know how the fabric is, you can buy pieces of fabric from their site also.
I think buying a dress online always is a bit of gambling. You never know exactly how it will turn out. I did do it though, but I keep in mind it's possible the dress isn't that beautiful, so I don't get disappointed.