Congrats on your light evolution!
First thing that comes to mind is that the COBs and T5s need to be at different distances from the plants, basically I think the T5's would get in the way of the COBs, being below them. I've used COBs as supplemental lighting to HPS, but never fluorescents.
As far as vegging goes, if you have a designated veg tent and wanted to use COBs, I'd stack it with 4000's. I really like vegging with those because I have limited height in my tents and they really keep the plants tight and low so I can veg longer.