never direct flow...really, in general for most fleshy LPS. Look at their skeletons. Large, sharp, exaggerated septa and septal teeth; any direct flow will be rather unnatural and tear them to pieces.
Thats not to say they like low flow though! Few corals do. Instead, here you want massive diffused flow. The convergence of stream style pumps in a large tank would be great here.
As for aggression, stonies aren't like softies or algae where they can dstroy each other easily without even touching (chemical allelopathy). Stonies are mostly straightforward; don't let them touch and give them good water quality and they'll be OK.
Now, you have to give them space to grow. Also they can put out sweeper tentacles soundly 10" long. So you really cant honestly stock too many of these in a typical home sized aquarium if you will fairly give them space to grow. I saw a fifteen year old Hammer that filled a 120 all by itself, save for a small octo that was in its shadow).
Think "one per 20 galls" and you will be in the ballpark for the 3 year picture.
Remember to feed them a small bit of minced meats daily or have a very large fishload; these are hungry corals that need fed a lot for long term survival.
cheers :)
