Given what you said about using the fret saw the view about the size of the boat is a good one. I'm still pretty fit and strong but I sold my 47" Huntsman 31 as I found it too big and heavy just moving it around the house nevermind getting it in and out of the water, even if you remove the superstructure.
So I'm now building one and a Swordsman, amongst others, at a scale of 1:12, so 31" and 33", which are a nice size.
I was going to change the big MFA 850 motor and lead acid battery as the performance wasn't very good but sold it before doing so. I've advised one or two folks on what brushless motor and LiPo battery to use but as their boats aren't finished yet I can't report on their performance. But the guy who bought mine fitted a similar sized motor (but not available now) and it goes well - see photo. The motor, ESC and battery work out pretty expensive though. And you need a decent balance charger for safety.
Be interested in what plans you're got for the big Huntsman - the only ones I know about are from the kits? If you do want to build at 1:12 there are plans available which I could look up?