So about payments:
You can ignore my advice, but the way I have always done this is holding off payment until I close the order. Splits change, people drop out, refunding is a PITA. So I would wait until Fri. night to pay up, to me or any of the splits. I will send out an email on Friday to every primary buyer on the list with instructions on what they owe, how to pay, when to arrive to pickup, etc. With the list online, some of that is overkill, but I am a creature of (bad?) habit so I will probably keep doing what I have been doing.
Remember if you are not the primary buyer on a split, you pay the primary buyer (via paypal if possible). Primary buyer of any splits pays me for the entire sack. Naturally, for any non-split sack you buy, you pay me as well. I pay our middle man, he pays the warehouse. Hope this is clear...