dust wont be a problem have you seen the dust they create when mixing gear. Is he on price though as might have the ump if not 100% ready to go at. Don't slow them down
Why is it wrong to dig foundations in your garden before the planning comes through. It's only like digging a hole in your garden. If the neighbours are on side and happy I don't think there's any moral quandary. Crack on if you're brave and confident the planning coming, if thats what you want to do.