When I make an instrument I work on one at a time. For me this is the way to focus on the particular pieces of wood, the model and style of the instrument, which translates into an instrument which hangs together visually and tonally.
The only exceptions are varnishing which often happens after I have started the next instrument, and joining the halves of back and belly. For the violin I have just started I hadn’t got a belly already to go, so instead of joining just the belly, I planed the joints of five bellies and two backs so that when I have a jar of special and rather expensive glue [isinglas] ready I can use all of it. So, last Saturday morning I glued all seven pieces, and then planed another two in the afternoon to use all the glue.