Yo,
That bass, if my memory serves me correct, is designed for the female form. So It mightn't balance correctly for a fella.
Generally speaking the top horn should hang over the 12th fret so it won't neck dive.
As for the neck. I would put a truss rod in. Maple is a hard wood but will still bend under pressure, especially if you don't splice it. You will get a better action with a truss rod.
I'd go for carbon fibre rods rather than steel. It's just as strong and lighter (balance).
What neck type will you be making? Fender style? Scarf joint?
Also, I'd use a ebony board if you making a fretless. Rosewood will wear out.
If you need any advice drop me a pm-Paul-