Hi Steve,
one thing to consider when planning your model is that you must have a radio system that can handle the functions you want to include. Motor forward/ backwards, rudder left/right (or backboard/starboard) and sound on/off can easily be handled with a inexpensive four channel radio. If you however want additional functions such as working radar, deck lights, navigation lights, lights in the deck- and/or wheelhouse, anchor handling etc etc you need a more expensive set-up.
In my diesel tug, based on a kit (Portgarth) from MMM in the UK I have all of the above functions plus some more and I have a radio with 12 channels and use them all.
Another thing to keep in mind: with many functions in the model you are likely to need some sort of power distribution board to provide the right voltage to the various "gadgets". As example the radar is running on 3 V and the main motors on 12 V so I have a board from which I get 3V, 5V, 6V and 12 V.
I think it might be rather tricky to add several functions to a Carson model - aren't they rather prefabricated and "ready to run"?
So unless you find someone to build your model I suggest you check out sites like e-bay, the buy/sell part of the Modelboatmayhem etc and see if you can buy a model that already contains the functions you want.
Claes