For your first question, I found that the tabs grab their recipes from a few of the creative tabs.
But after a bit more digging I found that anything in the combat creative tab is also shoved into the tools recipe tab and anything other than building blocks or redstone is shoved into the MISC tab.
so if you want your weapons to go into the tools recipe tab, you would have to assign them to the tools creative tab or the combat creative tab.
As for your second question, there does not seem to be a way to add a new tab to the recipe book. the tab list is final and there does not even seem to be a system to stop tabs from rendering off of the screen if there are enough of them, as the tabs are simply set to be under each other.