They will almost always take a picture with your own device. They will also take the PhotoPass picture, and you can look a them online later with no obligation to purchase. I've never had a problem with a CM using my phone to take a picture.
Absolutely, and with their camera as well. There is always a photographer there as well as a handler(who will usually be the one to take photos with your phone). I did this at the end April for Chewie. Wish I had my Han & Chewie magicband on that day.
Yep! We use them all the time so my husband and I can get pictures together. Both your camera and theirs if they have one. Heck, my husband and I have tried to take a selfie together in random locations and had CMs who happened to be walking past snap a pic for us.
I have had CM's kindly take photos for us, but if there is no CM around, I am sure someone nearby would be happy to take a photo for you, and even return the favour if they want one!