I built a Mini-Paw for my daughter, and to try my hand at building. As small as it is, I find it very sensitive to trim, but I am an overweight six footer. The most I have had aboard is myself and my five year old, so
under 300 lbs. I'm sure she'll handle 400 pounds in reasonable conditions, but will have to be carefully balanced. I have not towed her, but she rows delightfully and I can't imagine creating a problem under tow.
I am eventually going to enclose the area under the back seat as an air tank, you could cover the bow with
a small deck to help keep out spray. BTW, I don't remember what the finished weight was supposed to be, but I ended up much heavier. Learning curve, no doubt. Moving on to a Spindrift 12 so mom can come along. My 5 year old has rowed the Mini solo and she does fine. Unless you intend to have youngsters
using her, I would move the oarlocks farther aft than the plans show.