hi there Colin
Personally, I prefer to have independent drives on the paddle tug. To me, it gives a greater scope of use of the model on the water, rather than just relying on the rudder to perform turns.
The only concern I have with your system are the motors you are going to use. I am wondering, will they be up to it, driving the paddles without overheating? That is what you will have to watch out for.
Have a look at the photographs that I have put on - you will see I have used a 'toothed' belt drive system which also incorporates a reduction gearing - its about 6 - 1 ratio - as they say. Bear in mind the hull that you have is the same size as my hull and you will have the same access & available space inside the hull for modifying and changing motors and gearing,
If you do a web search for people who have built this particular model - I believe you will find the majority of them have used a gearing system of some form - either plastic pulleys and chain drive or tooth belt drive as I have - or a gearing drive system.
Hope this is of some help.
John