1. Can you do the pin trading in euro or is it just the America parks?
There is definitely pin trading! Plenty of cast members have pins, and there is also a pin trading shop in Frontierland that has a pin board where you can trade. It's not as popular as in the US; I traded with CMs all the time, but I don't think they expected it. It's definitely an option. Plus the CMs should all speak English, so that shouldn't be an issue!
2. Anyone know about the food for rough budget? I know it's really expensive over there from over friends that have been.
Don't eat at the table service restaurants. They are REALLY pricey. The quick-service restaurants will run you 10-15 euros for a full meal, including a drink. I recommend Hakuna Matata (Adventureland) or Toad Hall (Fantasyland), just from personal preference. If you really want to keep it cheap, there is a McDonald's in Disney Village. It's about a five-minute walk from the entrance to the park, so it won't take up too much of your time. I did that often (college student on a tight budget), and I would pay about 6 euros for a full meal.
3. How do the meet and greet works? Again I have a friends up school who have been and from what they say it works different to euro?
These are tricky. There are some organized meet and greets where you wait in a line and take your turn. Usually, the ones indicated in the program work this way. There are organized M&G's in town square (right before main street) and central plaza (right after main street). There is also the Princess Pavilion in fantasyland, where Anna and Elsa currently greet guests (sometimes, they hand out tickets for this during Extra Magic Hours, and they are usually gone by the time the park officially opens. Sometimes, there is a normal line, and that can get to 3 hours).
HOWEVER - there are also "spontaneous" meet and greets, where you basically wait in a crowd, and the characters pick who will be next ("C'est Goofy qui choisit," the cast member told me). Any time you're walking around the park and you see a random character, that is usually what happens. Basically, anything that isn't in the program is a free-for-all. If the park is really crowded, there will be more of these, and if you're smart you can slyly move up to the front of the crowd.
During Halloween, they had a bunch of villains do a meet and greet around the sword in the stone, every day. It was the craziest thing I had ever seen. You basically stood there hoping the character would pick you to be next. (and if you were alone, like I was, you had to find someone else to take your picture).
Sorry if that was really confusing! Let me know if I need to clarify anything!