Cannot help with DCC as I am dyed in rhe wool DC user, but I may be able to help with signals.
Signals do a couple of things -
1. - they protect against conflicts between two or more trains at junctions
2 - they tell the train driver which way the signalman has set his route
In sidings and yards (including the engine shed) where speeds are low trains usually move on sight or in response to hand signals from ground staff so apart from the signal at the exit which protects the main line and one on the main line which shows if the route into the yard has been set, you don't need to put many signals in there, if at all. Any lines which are used by passenger trains must however be signalled, so if your lines to the harbour see the occasional boat train you may have to consider a signal or two on them.
So you need to have a signal at each of the ends of the platforms of Tidmouth Station where trains leave to go on to the main line.
You need to have a signal on the exit from Tidmouth Yard.
You will need a signal on Duck's branch line where it joins the main lines.
On the main line where it first comes on from the right you will need a gantry or more likely a couple of gantries with signals which show which route (platforms, the yard or the branch line) which is being set for an arriving train. There appear to be five possible routes for the left hand main line (Duck's Goods, Duck's passenger, Tidmouth platform 1, run-round, Tidmouth platform 2) So the gantry for that line needs 5 'Dolls' which are the little signal posts that sit on top of the gantry. Siding routes would have shorter dolls than main routes. The right hand line (but only if trains can approach on it) would need 9 'dolls', In a real situation this signal would probably be a single post and arm but with a route indicator underneath which displays a letter or number selected for which ever route has been set.
This is an example of a gantry with four 'dolls'.
I hope this may help.