Not sure if anyone can answer that one unless they are in the business themselves. So assuming you have no prior experience in this field how about working it out backwards. What sort of premises are you going to use, what are your total over heads going to be rent, rates, power, wages, marketing, attending wedding shows etc. etc.
How much can you retail your dress’s for, what is going to be the mark up, how many dress’s would you need to sell a week to cover all your costs and make a profit .5, 10, 20 then maybe you can ask yourself if that’s realistic, what is the local competition like.
Hopefully someone with more knowledge of this area will give you a better steer.