generally speaking, SH do best in tanx that have some height to them (this is epsecially true if you plan on breeding them). 3x the uncurled height of the SH is a fair "rule of thumb". that being said, SH will use all of the horizontal space you give them as well.
as for aquascaping, branchy LR and lots of macroalgae help them feel at home and provide both hitching and hunting areas.
most pipes are more "horizontally-oriented" and do best in standard rectangular setups are fine. flagfins (
Doryhamphus sp.) and drogon-faced (
Corythichys sp.) are fine in mature reef-type setups with lots of LR, while gulf, northern, and alligators (the 3 most common species) do best in planted setups that resemble seagrass beds (
C. prolifera is a good alternative to true seagrasses, which require a DSB and bright lighting).
one thing to consider is that there are no CB pipes commercially available in the US, and i wouldn't mix WC and CB Syngnathids, esp if you're new to keeping them. Syngs have a real problem with bacterial infections as well as carrying pathogens to which one species is immune while another may not be.
to be honest, this is even true of mixing CB SH species, so IMHO, your first tank should be single-species TRUE CB SH. they'll come to you eating frozen and won't have to be treated prophylactically for parasites. do yourself a favor and ONLY buy TRUE CB specimens from a reputable breeder such as
http://www.seahorsesource.com Dan and his crew are THE best in quality and service, IMHO.
Beth (Peka here on RC) has some super nice erectus that she breeds as well, and is about the best hobbyist breeder i know.