500 thousand items?
I have to confess that I didn't realize there was 500 thousand dropshipping items available to start with, but if there is no listing fees involved, then you have nothing to loose by listing as many as you can ... apart from time itself.
In regards to it being profitable, well who can say one or the other. There are no rolled gold guarantees in this business, you're going into a super competive market using a low margin platform, so success is going to come down to the usual factors. Such as, competitive price, traffic flow to your products, providing a great service and then you still have issues outside of your control like economic factors and so on.
Trust me, this isn't an easy business to fid success in. So the best advice I can give you is to not take it too casually. It's a business, you have to treat it like a business.