Well, well I've just been diving this week and looking at pipehorses in temperate water. I would take that tank, get a thin layer of sand on it with two or three good sized pieces of live rock, orientate them vertically and try to pick pieces with caulerpa or other macro algaes of the right size/shape. If I couldn't get them I'd cheat and get some plastic vallis. I'd also go with the refugium. I'm seriously thinking of trying them as they are so easy to netcatch.
No corals with them - maybe you could research nd find some corals that come from a lagoon enviroment, but most of those are likely to burn a horse.
The tropical blue and yellow striped pipehorses look ultra cool, and are often quite cheap, and if you can feed them quite easy to breed .
As far as the nudis go I think they suck for the most part. They're typically impossible to feed as they are often ultraspecific, so id your desired nudi, find out what it feeds on and see if you can cultivate it. They'll usually do ok for a few months and then 'mysteriously' die as it takes simple inverts quite a while to starve to death.