I have had it altered with a prof seamstress. But I definitely think it is worth buying a dress online, saving money, and let a seamstress fix the details.
I was mostly worried because my cup size is 75E (danish size) - that it would somehow look inappropriate. However I have bought a "models saver" thing - I do not know what it is called - but it is the gel bra, that sticks to your skin. This way I look decent and have no straps at all. I'm only 160 cm tall, and I will wear TALL shoes at the wedding day. The measurements I gave together with the order were: 97-73-98 cm. This will give you an image of how a woman with curves can wear a dress like this.