I'm curious why you're proposing carbon fibre. It's not the first material that comes up when people are thinking of making a first flute. Are you planning a conical bore body, or cylindrical?
For the inside diameter of a cylindrical bore flute with G4 as its lowest note, you could start with 18 mm. This table refers to whistles, but there's no reason it doesn't apply to flutes, too:
https://www.music.bracker.uk/Music/Searching-For-The-Optimal-Whistle-Bore.html.
For hole layout, I'd suggest WIDesigner, available at
https://github.com/edwardkort/WWIDesigner/wiki. The overall length of the flute (if cylindrical) will be around 40 cm, or 16". There are other flute layout calculators available, but I don't have any links at hand.
Perhaps the most important piece of information, though, is how to cut the embouchure hole. With that, I can't be of much help.