Oiling first and gluing later, with some touch-up work round the join is normally the easiest way to work, especially if you are spaying. But if you glue the neck on first, it's not too hard to work with a whole guitar if tru-oiling as long as you've got the space to work on the complete guitar.

Spraying is a lot more awkward to do with it assembled, though it's more than possible to do if you've got the room to hang the whole guitar up when spraying.