I'm close to fitting the wood on mine, so not quite the complete expert yet , but my approach has been to concentrate on the areas which can't easily be got at once the wood is on, ie rear inner arches and flange extensions, rear spring hangers, boxing plate extensions, curvy chassis rail above front spring hanger (and spring hanger), rear boot floor etc. All these need to be fully paint protected and seam sealed as well as primed before the wood goes on. There's quite a bit of jiggery pokery involved in trial fitting the wood before final welding and painting.That is true, but I can halve the cost by fitting the woodwork myself. Is it ok to put brand new wood on with only a mere touch up of the parts which look bad?
I will completely spray my shell and panels before final fitting of the wood, but if you've got all the hard to get areas repaired and painted I can't see any reason you can't continue the rest on a rolling restoration basis and have a full respray later. (Thinking about it, it would be a lot better to have the ally panels painted before woodwork fitting, and best to have all the paint bought in one batch to avoid colour matching problems)
Have you got the Ray Newell/Steve Foreman "Morris Minor Traveller" book? Pricey, but essential reading before doing the wood.
Mark