More primer spraying has been done. This time we've gone a bit slower, put it on wetter, and it's giving much better coverage now.
Sanding seems to be OK for the most part, using 400 grit dry white paper. But there are places where we have sanded through the primer and back to the wood. Just trying to work out how to proceed with that. Maybe yet more primer. To the internet forums!
Most of the problems are going to be around the edges I think - it's way too easy to sand through to the wood there.