Having never done it myself, all I can do is comment on the parts I do know.
First of all, you can have areas of high flow, medium flow, and low flow, with hitches in at least the med. and low flow areas. The seahorses will choose what they want.
As for choice of corals, the determining factors are, do they have any stinging properties and are they likely to suffer from seahorse hitching.
In your case, with needing to be in high flow area then they are unlikely to hitch there, but, they could be blown into stinging corals if they inadvertently pass into the high flow stream.