Hi Darryl and welcome. For headstocks, 7 and 8 for me if you don't go for the traditional no.1.

As Drumerdude says, you won't find any glue spots with the naked eye (unless really bad). You need to wet the veneer, so that it goes darker and the glue areas remain pale. It's a very thin veneer and the PVA glue it's held on with is water-soluble, so best to use metho, white spirits or turps as the wetting agent. If you do use water, don't over-soak it.

Best of luck with the build.

Hopefully you won't find any glue spots (along the veneer join and just in from the edges tend to be the worst areas). But if you do, the best results are usually obtained by using a glue remover such as Goof Off. Because the veneer is so thin (0.6mm) sanding it off is fraught with danger and on some marks, the glue has soaked right through the veneer from the back. So keep any sanding on the veneer to a minimum and only use fine grit papers to do so, say 320 and above.