It's the biggest flying site in London so there shouldn't be a problem with room.
If you're driving be aware that there's no parking on the common unless you've already got a car pass from the
Kite Society. Most of the roads around the common are no parking and the parking in Greenwich Park is limited to 2 or 4 hours (can't remember which). Some of the side streets in Blackheath will be OK on the Sunday, but I'm not sure about the Saturday - and they're VERY hot at issuing tickets round there.
You're welcome to fly anything of mine, Keith but if I come by public transport I won't have much with me.