The brackets look nice. Very clean setup.
In regards to the chatter, I can’t imagine the y stiffening fixing that. I’ve also had chatter issues even with conservative feed and speeds. Especially through hardwood like oak and walnut. There is a sweet spot on the v wheels and delrin nut tightness that seems to do the trick.
I also replaced the washers that are in between the two bearings in each of my z axis wheels and that took a whole lot of slop out of them. If you try to twist your router side to side, you may see movement in the v-wheels or even hear and feel a pop. From another thread, these are the washers I used - My local Home Depot had them in stock.