I always sand the bamboo(mostly to remove cosmetic blemishes) and coat the entire frame with Epoxy. Ideally that should be lightly sanded and coated a with a UV resistant Varnish as Epoxy breaks down under long term sun exposure.
I actually didn't bother with that with the first few frames since the total amount of time that a bike is in direct sunlight isn't necessarily that long.
I just wanted to get riding it. It can always be varnished later.
I would still recommend coating the bamboo in some way. It's very hygroscopic and the more stable you keep it the less stress you'll get on the frame through moisture cycling.
You can get a surfboard building epoxy that is more UV resistant and that's probably a good shortcut.
I figure it takes about 5 ounces of 6k Carbon tow to make a frame. Depending on your technique of applying it you may use much more initially and then sand a good deal of it away.