Ian gets you to make the bulkheads first so that is a good warm-up on vac bagging.
Most of the time, the build only involves one layer of laminate so it is quite easy to do a decent hand lay-up without vac bagging, especially if you use epoxy. Use peel-ply on everything though.
Whilst your vac-bagged bulkheads will have a nice laminate finish, I think that the main benefit of bagging them is that they will be absolutely flat and true.