I would plumb it in using unions. That way it is easy to do maintenance on and you can create a blank if you ever decide not to use it. Or, you can start out with your blank and add the UV easily if you decide to.
What brand/model is it, and what return pump are you using? Unfortunately the hobby is littered with useless U/V units.
This is a very common thing I read, yet, there's no basis for it. Pods that go through return pumps are in pretty rough shape. If they survive the trip to the tank, fishes are delighted by a random pod shooting out of the return line and make a quick snack out of them.
As long as you don't plumb it in between your refugium and your display, I wouldn't worry about it killing pods. I run filter socks so any pods that take the trip down to my sump are being removed anyway. One big benefit from running a UV is that it will kill parasites and help mitigate risk from Ich or Velvet.
A UV filter can kill bacteria in the water column. I would definitely turn it off while adding a bacteria in a bottle product for at least a few hours. As for turning it off during carbon dosing, the more I think about it the more likely it is to be ok. While it will kill some of the bacteria you are trying to grow through the carbon dosing, the net impact is that it will take longer for the carbon to be consumed. This probably isn't a bad thing.
