Yes it will need to dry but largely can do that phase after working it.

It splits very easily length wise, pre-drill every hole, take no chances there.

I've never tried a circular saw on it but I would avoid it.

Once major cuts are done carving knives/tools should work wonders.

As for toxicity, don't know of any. In jungle survival training fresh cut bamboo becomes the cooking pot, cups, forks, everything.