yes its bamboo. the fret markers are scrap 1/4" copper pipe with iron wood centers. To make them do the following.
Use a hacksaw or jewelers saw to cut 1/4" sections from the pipe.
Remove any burs and then taper one end slightly so that it will go into the drilled holes without tearing the wood.
Prepare a section of the chosen material to fill the holes that is 1/4" x 1/4" and 6" long. Sand corners off of the material until it is round and just larger than the hole in the 1/4" pipe.
Taper a 1/8" section on the end dowel you just made with sand paper or a knife, so that it will fit in the pipe.
With a small flat faced hammer, hammer the dowel into a section of pipe, apply superglue to the metal and hammer it into the fret board leaving the edge of the pipe slightly above the surface of the fretboard.
Using a pull saw or a hacksaw cut the dowel off level with the face of the metal. cut from all sides to avoid tear out. After cutting the dowel off, hammer the marker down so that it is almost flush with the surface of the fretboard. Repeat as necessary.
When you have installed as many markers as needed, sand the whole thing down, so that the markers are flush with the surface of the fretboard. Keep checking the thickness on the sides of you fret board making sure you don't make one side thinner than the other.
I agree with MadGomer. It looks great the way it is and if the neck is the standard 1.5 inches wide, you won’t need it. Flat is probably better for slide anyway. And from your description, the fretboard is on the thin side, so you risk ruining it and having to build another one. It’s a good idea, but learn incrementally and save it for your next build. If you want to get more “professional”, consider adding a taper to a future neck, which may be more useful.
Let's step back, why do you want it to be "more professional"? At times like this I remind myself I didn't spend $650 on a Stewmac kit to build an "actual" guitar. It's a Cigar Box Guitar and not necessarily meant to look or be "professional". It's probably better when it's a unique artwork rather than something from a luthier's workshop. Personally, I don't want to be a guitar-maker, I want to craft artwork that I can get music out of. That might not be your goal. Maybe playability is more important to you, in which case, Chuck G. makes a great point, you have to think if the intended player is going to play with a slide.
I'm going to leave it as it is, since I don't want to risk destroying it. I hadn't considered that the fretboard on a guitar intended for slide needed to be flat. I have tapered it slightly from the nut to the bridge.
Hi, good move Ramson, what was not mentioned is that you would also need to deepen the fret slots also.
And it is normal to radius your frets prior to installing and maybe if slots are not a tight fit using glue in the slots.
I just mention this for next time.