Mike. Tricky proposition. It is bound to need a keel for a start in order to remain upright. I assume you would be doing a motor only conversion and not thinking about sailing it?
If I was doing this, I think I would build the hull first, with a propshaft in place, and then see how we are for weight, ie, are you going to be able to fit r/c gear in it firstly, without going beyond the waterline, and then seeing how much ballast you have to play with for a keel. Access will have to be thought about..removable deck sections betwen masts (say) or…? Motor and thus battery power will be very modest as these things pootled along, saving weight and volume inboard. Micro this and that r/c gear is very small and light.
At action stations (guessing here) does One assume the ship would be fought under steam alone? if so the sails could be furled saving weight aloft, similarly the ships boats would presumable by towed en-masse behind the ship also saving top-hamper. This would add a little something to the model on the water, towing boats..not yer usual sight.
Ashley