Love the L tank. That will look awesome.
For the UV, the slower the flow the better. UV is all about contact time, if its flowing quickly it is pretty ineffective, since the water doesn't have enough contact time with it to be sterilized. Most prefer to just split off a section of the drain pipe, and direct into the uv, with a gate valve to precisely control the flow. If the UV drain dumps into the return pump section there is little chance that you will be sterilizing the same water over and over. One less pump and cord to deal with that way too.
Since you have it mounted on the top like that, there will be another issue if the return pump is ever turned off. You never want to run the UV light without water in the tube, or the tube inside could become cracked and brittle, and will eventually leak. Then is becomes a serious hazard. If its mounted up top like that, the water will drain out of it when the return shuts off, which will leave the tube partially or fully without water in it. Generally you want it mounted so that both outlets are facing upward, that way the UV tube never drains.
Also for plumbing, be sure to add Unions, or even true-unions, where ever you can. They will save you in the end and make it easier to change or maintenance the plumbing