imo more is more.
the multi gives you soo much more choice in flow options alternating flow from different ends and even tidal effects.
one on a single would be ok but you wouldnt get the full effect
everyones selling something
tunze streams are great, as layton said if your going for something tunze the the streams are great.
in you tank i think two would almost be overkill (almost but not quite)
the controlable ones also add a nice randomness to the whole thing
but they are as you say hansen tank fittings, thats what they call them in the plumbing trade in america they call them bulkheads.
you might want to rethink the fluval, they are going to pump much against head.
just being trying to be sensible.
had i known before i started how much it would cost in $$ and time i probably wouldnt have started (at least for a few years)
oh and someone needs to get over to Joeblogs house and take a pic or two
ira i feel your pain with the rocks being too close to the glass, that is one of the prerequisites for my aquascaping