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Spend some time studying prices.  There are some things you can compete on and some not.  There is wholesale and then there is wholesale.  As an FFL you have already know that.  For me I use my capital (all cash) and grab deals as I see them come along.  To be honest 20k is not a much when you start doing stocking inventory.  When you say reloading equipment for benchrest and tactical guys you are targeting a very specific market.  That can be good and bad.  My advice would be to talk to the distributors and reloading company itself and see how much better pricing you could get on a large order.  As far as knowing what will sell and what won't, that comes with tons of research both personal and online.  If it were me I would look for deals and test the waters.  Spend a few k here and there and see what people like.  When they come by for the transfers have a small product line out and see if there is interest.  If it sits on your shelf for two months you will know.  If you have people calling you every other day asking about it, then buy more.  My personal business plan is for quick sales.  I try to make a profit for a week or two and then I sell at a breakeven and move on.  I do not like having my capital tied up on stuff that sits.  I would start with more of a shotgun approach and then narrow it down a bit as you find what you can move.