I was very interested in these and wonder if 1 cube would be enough(11 litres). If yes I might think about the trio.
http://www.aquaone.co.uk/betta-aquariums.php
http://www.aquaone.co.uk/betta-aquariums.php
By my math thats about 8.5g. Now I know its a highly argued point but I think a male betta should get atleast 5g to claim. My last male betta was in a 6.5g 11" cube and I thought that was about the smallest tank id be comfortable keeping one but some people have kept bettas in much smaller tanks. I guess anything would be a better life than the 4oz cups they are sold in though
Adequate, yes. I usually go by 2.5g minimum for bettas. But that is exactly that, a minimum. If you can find something bigger I think that would be much better and you'd have much more active fellows/galsMine are in a 5g and 10g, hope to upgrade the 5g to a 10g soonish.
You could always divide your own tank using craft mesh.
That looks like a really cool set of tanks
I'd do a betta in one, shrimp in another, and maybe a trio or 2 of guppies in the 3rd