Hi!
Hope I can answer your questions
1. There is a PTN every last Friday of the month. On the 27th the new flyer with pins get released and the date for the next PTN. If there is a pin trading day it will be announced on the flyer too. The pin events are normally 2-3 times a year. The last one was last month so I guess there isn't one coming soon
2. In the weekends pueble trading post is open. It's a little shop in Frontierland and outside are trading tables. I find more people trading at the tables in the weekend after a PTN. They also have a pin trading board at Pueblo. They used to have one at Harrington's too but not sure if they still have.
3. Popular are princess pins, cats, dogs especially WDI and DSF pins but there are enough people looking for HKDL/japan etc pins too. Best is to go trading when there is a PTN
4. OE pins are for sale in several shops. LE pins get released on specific days (always mentioned on the flyer) and mostly at the pueblo pin trading post. The LE pins that don't sell out immediately will be for sale in Harringtons on Main Street (there is a glass cabinet at the registers where you can see which LE pins are available) also some of the hotel shops carry pins that are sold out in the park.
5. I can't help with comparing to WDW because I've been there 17 years ago and can't remember a thing
Hope someone else can help with this question and maybe have some more info as well