Re: Reasonable weight for suburito?
A powerful cut follows a clean, straight arc. The integrity of the path of the blade, and possibly the speed as well, are more important than the amount of pressure applied to the blade once it meets resistance.
I don't know if its right to say you should use "no" arms when swinging a sword or if its just a certain quality of arm muscle power a good swordsman has, but certainly the goal of suburi is to learn to direct the sword with your center without your arms getting in the way and causing it to zig zag all over the place.
When you hear about "doing a thousand cuts a day" the point isn't to build muscles or develop strength. The point is for you to do the several thousand bad cuts that you must do before you can start doing good cuts. I'm sure there is an internal power story here.