I think you have it about right unless you do the wheelhouse as well. If you look at the modern AHTS which are a workboat just like this, they have a crew of around 14. So if you say two on the bridge, maybe 2 engineers and a cook, tha'ts not leaving many to be out on deck working and if they are doing shifts rather than 'all hands' you wouldn't need any more than you have.
You may want to move the guy from the bow though, not much is done up there when underway for safety reasons, in harbour its a different matter.