Actually a simple marine one would be nice. I'm a marine beginner actually - and I am so confused with all of the new plant life, macro-algae, and corals that my head is spinning. I don't know what stings or is hard to keep.
The problem with a marine one is that pretty much everything is terrible for beginners if they haven't researched and there is more of a diversity--for example, coral are a different ballgame than fish.
I've considered doing one focusing instead on species that are
good for new marine aquarium owners but even that is daunting with the various types of set-ups...FO, FOWLR, reef, etc. I may go for it if there's interest but there aren't many marine folks on here.
I will say this as general advice to you, though...I'd be cautious keeping coral with your dwarf seahorses (assuming that was the plan). Even if you keep coral that don't sting (keeping in mind that most of them do, they just can't all sting humans), many can release toxins that build up in smaller volumes (unfortunately, coral that can't sting are likely to have this defense for obvious reasons...they need SOME form of defense). And if you get a coral that really is "peaceful", it may be irritated by the seahorses hanging on all the time. Honestly, dwarf seahorses really aren't really reef dwellers in the wild. As far as I know (I'm no seahorse expert, though, haha), they live in macroalgae closer to shore.
That being said, there are certainly other invertebrates you could keep
. And macroalgae could work, too, do you have any currently? I had a lot of fun keeping sea lettuce when I was a beginner--not only was it pretty hardy but it grows fast and probably wouldn't be damaged by the seahorses. It's also edible
. Let me know if you need recommendations and keep in mind that you'll need pretty strong lighting to keep most species.