Its not a question of privacy, its a question of using the right tool for the job. This is something you presumably want to be found (at least, its value would be significantly enhanced if it could be). Putting it behind the spywall is therefore not a good idea. Its also something where you want people to be able to talk (unless I have misinterpreted “discussion”). A platform specialised for liking pictures of cats and posting one-word responses to same is not a useful tool for that task.
Unless you plan to get rid of the other sites, that’ll make it five different places 
While i understand your frustration with Facebook , it can be very useful for selling stuff, just my local area Facebook site (HBC) regularly sells loads of stuff, and no Trademe fees are paid, I have seen literally thousands of dollars of second hand items sell on there…but this would be non-profit page, and setup as a community page which are much better than a “group” page… more opportunities to blog etc… Since I suggested this , I must say I have had quite a lot of interest the idea, and many that have said they will use it, , and so far only one naysayer (but I appreciate your opinion). Not surprisingly a LOT of people who attend Cons and are looking for costumes use Facebook everyday, and I mean everyday, do they use Diatribe everyday? Or maybe the other sites like Paddywhack and Jackie’s proposed site everyday?? It would be nice maybe if they did, but it’s somehow doubtful. The beauty of having one Facebook page to link all others from (Which can be easily done with a Facebook “community” page) is that people go to one place , and access all others from it… As more costuming and Armour sites are found/made they can be added (Admittedly the same applies for Diatribe, but as I said before it’s not used everyday) We can have people like Beth St.Clair (already agreed to help) and others who are costumers/Armourers to describe how they made their costumes, have special areas for photos (with or without links) etc. Also, please don’t think of this as Yahn’s Facebook page , it may be my idea but I am fully happy to get it off the ground and have others as admins or even Lead admin if they wish. I am not one who would wish to be King, I don’t wish this at all, but from talking to others I saw a gap and thought, let’s fill it… Then of course there would be the Loan/Borrow section, which I suspect would be used regularly around Cons… My idea was that we trial it until Teonn, see if it is used , and works well, If not, Can it. I am happy to set it up, or support anyone who wants to host it on Facebook, but am happy to discuss it further…
My site is designed with a global audience in mind and I’m not really going to set it up as a place for individuals to buy/sell/swap stuff. I’ve worked in the world of e-commerce/trade (Amazon.com and TradeMe) and the last thing I want to be bothered with is dealing with disputes from people whose swaps went wrong! 
So, yeah, I’m in favour of the FB group, but maybe focus on one thing and do it really well (swapping/loaning gear) rather than try and be all things (costuming guide, tutorial guide, whatever…)
I’d also suggest you hold a yearly or bi-annual “clothing/gear swap” event which you advertise via the group (and Diatribe). This would be advertised via the group but held in a physical location - i.e.; you show up with a pile of stuff you want to get rid of and negotiate sales/swaps with other people who have also brought their piles of stuff!
In between the official, scheduled events, encourage people to use the FB group to offer up/ask for things to swap, loan, etc …
As has been mentioned, ebay is already a good platform for selling things on an international level. TradeMe works well locally. Yes, they charge fees but they also offer services such as rating sellers, some degree of assistance if trades go wrong, etc … things an administrator of a volunteer-based site really wouldn’t want to get involved with.
But what there isn’t currently is s swap/loan site, so that’s why I’d suggest you focus on that. And while you can use Diatribe for it, I think the functionality of Facebook makes it the better platform (even though I hate FB myself! )
Thanks for your input Jackie… And yes , a lot of folk have also agreed that Loan/Swap is the best way forward for the page, but I still have quite a few that want to sell stuff too, which i think would be perfectly acceptable, It’s really just a case of Build it, and see if they come.Was going to call the page “LOAN BUY SELL SWAP DISCUSS” LARP COSTUMES NZ" but may just cut it down to “Loan Swap Sell Larp Costumes NZ”, as I said before , if it isn’t being used much , it will be deleted… It has until Teonn to prove itself worthy…
Yahn Darkwood