Hi Silurian
Welcome to ModelboatMahem. Here you will find a very helpful group of like minded people who can help you with your boating queries.
I have built the Boston but at a scale of 1:32. As she is not a 'speedy' boat, I would agree with you that power before speed is the best approach. The ideal motor might be a 545. This has many poles and will travel slowly but has the power to move her gracefully thought the water. As to the Prop size, then I can only guess as to which one to use. You may like to start of with a 45mm diameter if you can get it under the hull.
You may also like to post your own blog on this site and don't forget that we like loads of pictures.
Hope this helps,
Ken