The raw hemp fiber will work the same as the finer fiber. I am now under the opinion that twine may leave air pockets or pockets of resin void of fibers. I think you can make a stronger product with fiber (make test pieces and destroy them to draw your own conclusions).

I personally find TOW line is easier to work with than cloth. I am unsure the differences in strength.

Sand the enamel skin off of the bamboo wherever you want the resin to adhere.
Cutting through the skin before you cut the tube will lessen the chance of the skin splitting.
Wrapping the cut in blue painter's tape before cutting will also help.

Bamboo is not perfectly straight. I think you will still have alignment issues if you cut up an old frame and try to make an internally lugged frame.

Use off the shelf (Nova, Henry James, Paragon Machine Works, etc.) metal parts (head tube, bottom bracket, dropouts) and mount them to your jig so they are properly aligned. Fit the bamboo between them.

Miter the bamboo the same as you would using metal tubes, then tweak the fit by sanding the miters so the bamboo lines up as you want.