We will be baking in a detailed sizing chart soon. The chart will also have the closest analogy interms of fitting wrt size to a popular brand ( Zara, Armani ..etc). In terms of returned inventory - donations were one of the routes we were thinking.
If you give directions to the buyers on how to measure themselves (or ask them to go to local tailors) you could have the pieces custom made for a fraction of the price of what it would cost in the USA.
I know it adds complexity to the process, but if I had a profile where I could input my measurements, buying would be much easier, would significantly reduce the return rate and increase my satisfaction.
I really like the concept you are going for. Good on ya!