The first stage will be empty of fuel and is basically a big empty metal balloon with a huge lump of metal at the bottom. The centre of gravity is very low, so

The first stage will be empty of fuel and is basically a big empty metal balloon with a huge lump of metal at the bottom. The centre of gravity is very low, so while it looks really unstable it's much less bad than it looks --- like a double decker bus. OTOH, as you say, there'll also be a huge amount of windage from that big empty metal balloon... SpaceX seem to be competent, so I assume they'd factor this in. I'd be interested to see an analysis, though.