What type of veil would go with this dress and what type of undergarment support?
I'd personally go with a cathedral-length veil to complement that awesome train. Maybe with matching lace trim if the designer makes it?
Also, for my dress, I had a nonexistent back, but needed more support than just added cups (according to the people who were profiting off of me), so I bought a bustier that worked with the front, and my seamstress cut the sides and back off of that, then sewed it into my gown. Good luck!
Given the back - sewn in cups are really your only option which already may be part of the dress' construction. Or, they have a "tape" style that you essentially tape to your body to hold things in place. Not ideal though..
As for veil - a lot really depends on the type of style you're going for in terms of personal taste/preference. A fascinator or hair band (similar to the waistband) with a simple round cut of tulle (attach a couple bobby pins with fish line to hold it on) is more than enough - because you don't want to overdo it. That's also about $5 in materials tops...