If you are experiencing problems with supplier response time, I would recommend trying to call them, not use email. While suppliers should use email as a priority, the fact is that many just don't and email inquiries can some times just be completely ignored, if not have an extremely long response time.
So calling a supplier is the absolute quickest way to get a response.
In regards to recommending a supplier, I can't really do that, other than to say that all suppliers within our directory are fully verified and recommended by us for members to trade with safely.
In regards to what products to sell, well that all comes down to market research and unfortunately there is no quick way around that.