Since CN is not a big challenge as long as CW can knock the adds off, I normally take my GF/GWF friends to my group and play CW myself. So far, I have never had any trouble with clearing dungeon but some random DC refuse to join my group after seeing there are GW/GWF in my group LOL.
No, it never grants 100% instant craft. I have tried with 4 purple assets which grants 160%(40x4) crafting speed, and it only reduces only about 2/3 of the total time. The extra speed from assets does not simply subtract the time like that. I think it's multiplication or so.
I thought it was an interesting crafting system... but it's getting dull and dull whenever I craft. Currently, I'm on lv19 tailoring but now it requires 40k exp to level it up and crafting items grants me only about 500-800 exp. In the end, I have to check my profession tab every hour to make useless stuffs and waste my AD…