Without a bit more specific information, I think your question might be tough to answer in any kind of specific sense. Things like unit price and how much capital you have access to are going to have a lot of weight on the answer to this question.

But! Regardless of all these details, I think the best strategy is to start with a relatively small, to medium-sized order, considering how expensive or inexpensive your inventory is. Do this to test the waters. If you avoid buying a whole mess of stock, you're not putting yourself at too much risk: buy a cautious enough amount that you won't cripple your pocketbook if nobody buys anything. If your stock DOES sell nice and quickly, you can order more and list again!

Hope this helps.