Put your belt sander aside for the time being and don't be too quick to prune that handle.
Your blade profile reminds me of an old Kershaw folder that I have buried in some kit.
Just to say that it's very useful in shape.
Size:
Palm up, in a fist-grip of the handle, the tips of your middle 2 fingers should just touch
the fat ball part of your thumb. I learned this for wood carving tool handles, elbow and D adzes as well (Kestrel Tool.)
For my big hands and long fingers, any handle blank of 7/8" x 7/8", rounded off, will be very comfortable for me to hold.
3/4" is the lower limit ( arthritis pains) and 1" just seems fat and unwieldy. Yeah, I was surprised, too.