[Derek UK]

Unless you're really good/experienced, the paint shop will invariably find fault with your work and do it over again. They will rub down the entire bonnet with maybe a thin skim of filler here and there, and/or some primer filler. You could do some extra work on the bulkhead and the underside of the bonnet but they will also prime and flat those areas too before the coat of blue so again I would leave it to them. If in doubt have a chat with them, but in theory at least they are the experts. Keep them happy. If they are the same shop as did your paint before they should at least be able to do a good match on the colour. Good luck.

I read this before I saw your other post saying you were going to DIY it. You should be able to get a reasonable finish in the engine bay and the underside of the bonnet if you use quality paint and aerosols. Maybe you have automotive paint supplier within reasonable distance that can supply and also make up some cans of the correct colour. Think I would like to get the outside of the bonnet done professionally for best results. It can all be back on the road with a big primer patch on the bonnet so you can drive it in for the final touches.