Hi George,
Looks like this tank is going to be a stunner !
I'm undecided about the 3 or 5 stone design, but I do prefer the way you have the larger stone positioned in the 3 stone layout, the shape just looks a little more natural.
Not sure why, but I think it's becuase in the 5 stone design there is more of a dark shadow and it is central in the tank, acting like a 'focal point'.
As regards the HOB filter, I've been running one for a few weeks now and they are ideal for nano tank. I did have a problem with the media to start with, but got a few tips from Moody and it's fine. Interesting that the place that sell the filter, doesnt seem to stock replacement media for it .... not a big issue as DIY media as Moody has done is far better.
The only problem I have with it is that it doesnt seem to push the CO2 around the tank quite as well as I'd hoped, maybe this is down to the water flow around the larger rock in my layout ..... If Moody's is doing it Ok then I think I need to experiment with the filter position !
Cheers
Al