IME, yellow-banded pipes (D. pessuliferus) tend to be a bit more touchy than the other flagfins, probably because by the time they get to you, they're pretty thin, and their digestive systems are on the verge of shutting down. Like SH, pipefish lack a true stomach, and thus, cannot hold food for digestion (they hunt pretty much constantly). The other flagfins seem to come in with more weight on them. If you have a QT/Training tank with a teeming pod population, you might be able to get them over the hump so you can wean them onto other foods (frozen mysis, cyclopeeze, roe).
A SH/pipefish tank is a great idea, however, it's a crap shoot when it comes to mixing Syngnathid species...sometimes it works, sometimes one species dies, sometimes both die. This is especially true if you mix WC (there are no CB pipes in the US) and CB Syngnathids. The reason for this is that one species may carry a pathogen that they're immune to while the other species is not.
Personally, I'd go with either one species of SH or pipes until you get some experience, and then branch out from there after you learn their care and habits.
If you can, ALWAYS get TRUE CB stock from a reputable breeder (Seahorse Source is tops, and Beth [Peka] also has super nice SH) or hobbyist/breeder. They will come to you eating frozen mysis and conditioned to aquarium conditions.
Biggest mistakes peeps make with SH:
1. Keeping them too warm...even tropical sp. should be kept at < 74*F due to their propensity for contracting bacterial infections.
2. Keeping them with fast-moving or stinging tankmates.
3. They MUST eat at least once a day, twice is better. Plan on one cube of mysis per pair. Some peeps skip a day every so often, and that's OK to give them a fasting day, say once a week.
Other than that, live macro algae is your friend...it gives them hitching spots, hunting spots, and general comfort. It also looks nice and aids in water quality via nutrient export. We use live macro in pretty much all of our setups, SH or no.
HTH
