i have been watching the paypal issues fairly closely since they issued their new policies earlier this year. I also just ran my own first group buy. i did not post this earlier because it is a bit long-winded, but maybe it can help. here is my take on it:
i called paypal a few months ago to try and get some information on their new policies, since i had been hearing about people's accounts getting frozen. the rep i talked to said that there is a random algorithm and, "they dont know what triggers it." maybe she just couldnt tell me. I asked some of the people whose accounts got frozen about their experience. from what i can piece together, it sounds like people with "business accounts" who are invoicing international orders, and receiving many thousands of dollars each month - are all more likely to get flagged by the system. It is still unclear to me what happens when you are "flagged," but the rep i talked to said it is based on individual transactions, not entire accounts. she also said that if a transaction gets flagged, all i would have to do is go in and mark it as shipped. tracking or receipt is not required. not sure if that part is true, though.
jdcarpe is probably the worst example of someone's account being frozen. i really feel bad for the guy, and him being down has really affected the community. (he's the guy who used to do the monthly geekhack keys) i hope he doesnt mind me sharing, but i think his account is still frozen until he can provide proof that some of his orders have been fulfilled - and a couple of those are international orders that are not easy to track. keep in mind that he was running multiple group buys at the same time when he got flagged, so probably many transactions. barebones stormtrooper will probably be more than $15k moving through your paypal (150 MOQ x $100 + shipping?), so this may affect the GB. my group buy did not have any issues, but i did not have any international invoices, and i think it was not even $5k for everything. keycap sets are spendy
worst case, is that you refund everyone the money and we start over with a different means. that could deflate the interest and cause some people to pull their orders. there are other options to consider, and i would suggest asking some of the other prominent group buy organizers for input as well. LunarisDream, JDCarpe, and Shadovved were good resources for me - very helpful guys. you may also consider asking a vendor to help, though that may add cost and it sounds like many are busy with other sets as well.
tldr; paypal has enacted new policies to cover their asses on transactions. it seems like they focus on individual transactions that fall within certain parameters. this may or may not affect this group buy (or any group buy for that matter). i suggest you call paypal and ask them what to expect. it might also be a good idea to talk to some people whose accounts got frozen and ask them what to expect.
like i said, i have faith in manifex to deliver on this, but paypal is another issue. it may be in all of our best interest to at least consider other payment alternatives if paypal cant guarantee their services. still hoping to see this set get made!