Depends on your quarantine practice, lighting, feeding habits, etc. Many tanks run exquisitely without one, some run permanently and others run intermittently.
And get a recirculating skimmer— no sump water-level worries.I am not sure they make an HOB UV that will really handle 140 G. Of course, you can hang anything off the back of your tank, but the big UVs are heavy. If you have a place to mount it, Lifeguard makes pond/aquarium UVs which are significantly (50%) less expensive than those offered by the mega dealers, particularly if you by from a pond/aquaculture supplier rather a reefer outlet. "Just slap reef on the label and double the price". There is a long thread here on R2R regarding the Lifeguard product.
It will help but might not kill cysts . More is better. Buy submersible bulbs and create a compartment in your sump for them. It'll work.
After 8 month I'd be concerned with efficacy of the bulb. Most decline after 3 or 4 months. Good lung finding the right combo for your tank. This setup does look really nice.I bought this when I had a bad algae bloom for a two week period on my 130 gallon, it eliminated the bloom overnight, paid under $100 and it's been going non stop for 8 months.
