Thanks for all the feedback, guys!
Tony - thanks for the suggestions - I've tried them and I think they work!
TDI - glad you like the rock - so do I!
James - it may not be obvious in the pictures, but the substrate rises from 1" to 5" plus. The stone is seiryu stone. A couple of small spurs broke off in transit, and the revealed surfaces seem very different, as if the stone has a surface patina. So I'd be reluctant to break it up further. It may not be obvious but I've got five pieces, and they seem to sit together nicely, mimicking deeper fissures between individual rocks. so -
Baron von B - your messing with paintshop is outstanding, as you've created a sixth rock for me to play with! But in truth, you have made me consider opening up some of the gaps between the rocks - we'll see.
George - yes I did have a hardscape idea all ready to go, but even with TGM's vast selection I couldn't match my ideas to their rock reality. So I went with the flow instead. And thanks for the planting comments - safe is what I need to start with, so that's good. Oh, and thanks for bunging this in the Journals section.
Having put the Eheim pipework in, I can see why many loathe it - I'm finding it hard to resist the temptation of going straight for glassware, and hang the expense!
Also I chucked the idea of using two big Eheims and went for a single 2180 - just hope I don't wind up needing a powerhead to increase the flow. The money saved was blown on a better luminaire with MH and some rather pink T5s. I'll post pictures of the cabinet when I get home - I'm away for a few days right now.
Cheers all
Paul