Hey man, welcome to Canreef
You do NOT need a UV sterilizer. That is the biggest crock going... if you don't overstock your tank, feed your fish properly, have a big enough tank for said fish to begin with, and perform regular maintenance (water changes, etc) your aquarium fish shouldn't have diseases any more than ocean fish.
As far as flow, for a FOWLR, since you don't have any corals, you should be good with anything around 10x and up. I wouldn't count the skimmer as 'flow', nor the canister (unless it's large, like 500 gph, and empty so it can actually move that much water).
I personally would get rid of the canister altogether (you don't need it if you have enough live rock, unless you want it for mechanical filtration or a place to put carbon and such... more work than it's worth for these uses, IMO)... but that's a discussion for another thread.
The best advice I can give you here is READ READ READ! Then you can decide for yourself if a UV sterilizer is right for you.