It might be to early to cut it right now. You will know in a couple days if it is mature enough, because it will start to shrivel longitudinally. If it still has smooth sides after a week you should be alright. That being said, I'm afraid it takes several months to cure properly and harden. I have made arrows in as little as 3 months successfully, but any quicker and they don't seem to hold up. As far as foreshafts goes, it depends on how much FOC you want. I prefer dogwood and maple (diffuse porous and dense) but have had good luck with ash, osage and even black walnut. I have used ramin wood dowels when in a hurry, but they do not hold up well at all. When fitting the foreshaft to the cane, make sure you have good shoulder contact and that it is also contacting the node inside. Sinew wrap the shoulder and the node to prevent splitting. Same thing on the nock end make sure your nock insert is touching the node inside. I like to have the nock end node, right where the back of the fletching will be tied on with sinew. That way the sinew is reinforcing the nock as well as holding the feather on
. If I have confused you on the foreshaft fitting, look at my 'quiver friendly atlatl dart post' I use the same method there, just bigger. My laptops down so it might be a while before I'm back on, I hope this gets you started anyway.
Josh