Hi. I visited DLP last year and have a few answers to your questions just based on my own experience.
The main trading board is at a gift shop in Frontierland called Pueblo Trading Post. I went 5 or 6 times in the day (waiting for cast members to shift so I could trade more
) and they always had at least 4 or 5 options for Paris LE pins. The board is organized and divided up by edition size.
When I went, at the big trading board, they strictly enforced like-for-like trading only. When trading for an LE pin, your pin must be
less than or equal to the printed edition size of the pin you are trading for. So if you wanted an LE 500 off the board, you could trade your own LE 500 or LE 200, but not your own LE 800. Also, multiple employees there would not let me trade a US parks hidden mickey or open edition pin for a Paris hidden mickey pin. It HAD to be Paris hidden for Paris hidden mickey. Paris hidden mickey pins do not have a hidden mickey on them. They're officially called Paris cast lanyard pins. They have the Paris logo stamped on the back and are released in series like US HM's.
Also, just a note I did not attempt to trade any Loungefly pins in the park.
I only had any kind of issue with what logo was printed on the pin at the big board. In general, the CM's were understandably not familiar with US pins. I wanted to trade a DSSH LE 400 pin for a Paris LE off the board. Paris LE's have the pins number out of the edition size printed on the back (so the first pin of an LE 500 pin made has 1/500 printed on the back, the second has 2/500, and so on) and of course DSSH pins don't have that, so the Paris board employee was confused by my pin. A random person near me in line accused it of being a scrapper when this was happening (I literally bought it from DSSH???????) but the employee ended up approving it. That was the only moment of friction I had and it worked out fine.
A handful of castmembers in gift shops also had lanyards/felt squares with pins for trading. I found individual cast members to be much more lax about what we were trading for. But even individual cast members had what I thought to be really good pins - mostly Paris OE's & Paris booster pins & Paris hidden mickeys that they were thrilled to trade for any Disney pin.
Also, people will hang out with their books at tables by the Pueblo boards. I traded with a bunch of other guests and they LOVED getting US park pins. I traded for a lot of Paris LE pins that way.
Just let me know if I can shed light on anything else. Overall I really enjoyed pin trading at Paris.
And I spent loads on buying pins as well Lol! If you're interested in shopping for pins, check every gift shop. The selection seemed to vary widely across the park, though Pueblo had the most options overall. Each of the big gift shops had a handful of LE pins (when I was there, they had a bunch of the Genie in outfits series) and those varied between shops. And if you see ones you like, I would recommend you buy them when you see them, even OE's - I noticed CM's did not restock the pins throughout the day, and by the end of the night, pickings were slim.
