We don't know anyone else in person who has a kid with celiac, but we do have friends who have been very supportive. They make sure that there is food our son can eat when we go over to visit. And my son's friends know that he can't just eat whatever they are having. He's older though (11 now, but 8? when diagnosed). We have found an active ROCK group in our "area", but it's in the city 3 hours away, so I haven't actually met the people posting on their facebook page, for instance.
2 is hard - there is food everywhere. My suggestion would be to show up at playdates with snacks to share with the other parents and kids. Ask if they would mind putting away the cheerios during the playdate, so that your child could eat what everyone else is eating, too. And hope that over time, your friends "get it". Sometimes you just have to forceful and explain what gluten does to your child. Not everyone knows what celiac is or that minute amounts of something (like the cheerios everywhere) can make your child sick.
You don't need to have friends with celiac kids or gluten-free kids to still have a safe and accepting environment for your child, but you do need friends willing to support your efforts to keep your child safe. We have found most places we take our son have been great (school, day care, friends' homes, relatives houses, etc.), and some want to be helpful but need help knowing how to do that. Sometimes, just showing people what is and is not ok (and lots of "regular" foods are gluten-free) helps them to know what to have on hand when your child comes over to play. Maybe the next time you have everyone over, put out some yummy gluten-free snacks that fall into the "regular foods" category (fruit, veggies, cheese, chips & salsa, etc.) so that people start to realize that you don't need to go to great lengths to accommodate eating gluten-free, but you do have to pay attention to it.