like andy said, it depends on the fire. the graham cracker will burn and stick to the foil in no time over high heat. you really just need to warm them until it starts to melt. it helps to flip them a few times to heat them evenly.
I put my graham cracker squares on a plate, with chocolate on top, then I roast a marshmallow, put it on the chocolate, top with other cracker. Sometimes I will place the graham cracker chocolate next to the fire, so it warms a bit, but the heat of the roasted marshmallow melts the chocolate just fine. I like to use the thin Lindt bars, creamy milk, dark with orange, dark with sea salt, for variety.
no, it's quite simple! Especially if everyone has their own marshmallow roasting fork. If you have a couple of kinds of graham crackers and chocolate available, everyone can mix and match up their own combinations.
and if you can make your own marshmallows, even better! Instead of vanilla, I like to use gran marnier. The toasting of the marshmallow really brings out the flavor!