The VHC themed buffet sounds like a lovely idea, but ffs don't call it a BLW buffet. If you send that out on the invitations you can be guaranteed to get mass eye rolling at that one. As so many have said it's just food.
Please provide paper plates. I'm cool with children pinching bits of each other food, but not about them (intentionally) eating off the floor like dogs and eating food that's been under one anothers shoes/leaky nappies. Maybe you could lay out picnic blankets so they all still sit together, but in a slightly more organised way, with their mostly own food to go at.They will still enjoy themselves and the parents will be more relaxed and like you more. 
I run a playgroup, we have the occasional messy play activity day. It goes down well, we don't mind cleaning up, the parents are glad that they don't have to do it at home.
However, food is not messy play. It's not a toy. I did BLW with dc3 and dc4, although I didn't know it was called that then. I just couldn't be arsed with all the preparation of purees and didn't have the energy for endless spoon feeding. I still taught them manners from an early age and encouraged them to eat nicely.
At playgroup, every week, including after messy play, the children sit with clean hands around a low table in low chairs and eat toast and have a drink. It's all very civilised, even the younger ones sit and eat nicely as the copy the older ones.
It would have really pissed me off if someone had introduced the idea of food being a messy play thing.
You did want to know what the other parents will be thinking, that's what you've got from this thread!
One thing's for sure, it will be talked about for years to come, though maybe not quite in the way you were hoping!