um, to be honest...what I would strongly advise is to try selling a few pieces online...have a good web designer create a sight for you and upload pics of all your items for sale & see how it goes...how it sells...give it about 2-3 months...if you see that it is really going well no harm no foul...start looking for a store & keep creating!
you want to see if it goes before you take the risk of all the rent, designing the store & loosing so much money before people even get to know you...only to close it up god forbid 3 months later due to no customers! as for department stores...once your store is a hit & you start publicity & marketing strategies you will have eating out of your pocket!
hope this helped! good luck!
Start your own store. You'll sell more, and once your business is well known, other department stores will want to sell your line.