What is the registered land use where it is parked? If it's agricultural land then you are most likely drawing attention by use of a domestic vehicle (planning worry about people setting up temp homes on agri land as a prelim to trying to move in permanently) and you might get away with locked/covered winter storage but not with use.
The use you're making of the fire and groups will have an entire set of planning worries for them - safety, groups of kids fires, smoke, noise etc. Put the two together and you appear to be moving in and starting a business fraught with safety issues on what is not your land and has clearly been raising questions/complaints.
Yes planning can be a dogs breakfast but look from their point of view, or the neighbours to that area, and see what it looks like from the outside. The setup sounds similar to things they actively don't want eg a gypsy campsite, a gathering place for local kids/teens to hang out and make trouble, and a potential fire/noise/smoke pollution risk for folk that own the homes around.
If someone was 'storing' a van on my neighbours land I'd have no issue but start all those activities and I'd be worried myself. You may be doing no harm but you can maybe see why some folk would be concerned and address those concerns instead - provide locals with information about your activities with kids and fires, or move the van to simple storage away from the fire/group area and continue the activities or vice versa to half the problem and work out what might actually be feasible. Council might even offer you a site for the 'arts for kids' activities as they are encouraging those in many places, but with the H&S issues and risk assessments etc as part of the setup process.