With all due respect, the people with lots of prior tank experience can be the worst ones to take on seahorse keeping. At least those that haven't kept tanks before will possibly do sufficient investigation to make them more aware of possible problems.
I was one of those with experience that learned the hard way, costing needless seahorse lives in the process. I'm 75 now, keeping tanks since grade 5 many decades ago and switched to salt water tanks in Jan 94. (9 tanks smallest 40g) When I started seahorse keeping around 2003 I thought I had sufficient experience to have few problems in my hobby expansion.
It turns out that keeping seahorses is nothing like keeping normal salt water fish. I've never kept ANY marine fish that was SO susceptible to bacteria influences that seahorses are.
I know of nothing in animal husbandry that will contribute to success at keeping seahorses but hopefully there will be something that helps.
Hopefully you can get replies from other keepers that have used other methods of filtration as I've not got into much other than canisters, HOB's and my present methods.
As for canister filters, I originally didn't realize the importance of frequent cleaning and when I did, the at least weekly cleanings of the detritus build up was just too demanding in the long run. In time, I ended up skipping a change here or there and that just meant that it took longer for the bacteria problem to show. The media didn't require frequent replacement as it was after the detritus filtration part.
Once I switched to powerheads with quick filter attachments that could be very easily cleaned every 3-4 days, I was much more successful.
I have no experience with peppermint shrimp larvae as the only shrimp I had in them was cleaner shrimp that ended up being torn apart and eaten by two of the female H. reidi.
I suspect the pep larvae should not be food for the seahorses as adults because over fifteen years of seahorses I found most wouldn't even entertain even baby brine shrimp.
The do however take to enriched adult artemia that I've been raising a decade more than I've kept seahorses for. Small foods if they DO partake of them are not of much value because of the inordinate amount needed to provide sufficient nutrition.
I have NO use for UV in adult seahorse tanks as the majority of destructive bacteria like the vibrios species are benthic and don't pass through the UV like pelagic ones that are not usually a problem for adults in our tanks.
Dan Underwood of seahorsesource.com only recommends them for fry systems as far as I know.
As for sumps, I have one for every tank but for me, the importance of the sump is just to boost water system volume to make it more forgiving when something does go wrong, and, to place most of the live rock which I don't like in the display tank as it makes it even harder to see the seahorses when I want to, and, makes it more difficult to clean as rocks trap detritus VERY easily.
I don't think the seahorses really care what the contents are as long as they can't be damaged, and have sufficient room to do their thing. My tanks don't have the nice look my coral tanks did but they are easier to keep alive with my now limited capabilities.
If you DON'T get enough feedback here on filtration systems, you could post on Facebook's Seahorse Keeping Made Fun or Seahorses and Pipefish.
https://www.facebook.com/groups/seahorsekeepingmadefun/
https://www.facebook.com/groups/Seahorses.Pipefish/