The only fee charged would be a 0.1% withdrawal fee, all trading volume would be no-fee
It is not sounding as good idea as it seems you are missing out your big income stream.
The usual practice among all exchanges is, charging for each and every trading and then there will be no withdraw fee (otherwise only network fee).
For example if some trader deposits some $100 worth of bitcoins and trades some 10 times and then withdraw only $40, he might have used all your resources but you are not charging anything for his activity but to the amount which might console him after some frustrating experiences.