For a 24g nano cube I would definatly do a pair of true or false percula clown fish and a goby/pistol combo and that would be my limit.
You could also consider a purple firefish with a 6 line wrasse as your limit.
Lawnmower blennys generally need larger systems due to their eating habbits, I would skip this.
The green mandarin is definatly off limits for a 24g. I would not even put one in that eats prepared foods.
The cleaner shrimp and sexy shrimp would be good, but I would skip the fire shrimp, they are rather shy and would be overload in a 24g.
As far as coral goes, the nanos are perfect for softies. You could have some nice polyps with some shrooms
, xenia and some leathers. (look into activated carbon, I like to run it on all my tanks, many soft corals release toxins into the water, and is IMO
, important on skimmerless systems)
The absolute most important thing IMO
when running systems like nano cubes is to not over feed or overstock. You can ruin the water quality rather quickly and have all sorts of algae problems. I like to run grape calupra macro algae in the display to help control nitrates and have had great success on my moms 24g reef and my 6g mantis tank.(this is more pratical in smaller systems because you have to be an idiot to let it get out of control)
I would consider a 3-4 inch sand bed with a dozen or so nassarius snails to work it nicely.
Also get plenty of rock, 40lbs in the display would be nice, with a few lbs in the back compartment would be perfect.
If you want my personal opinion, I would setup the tank like this.
4 inch sand bed
48 lbs of LR
12 nassarius snails
12 margurita snails
2 true percula clownfish
1 pistol shrimp
1 cleaner shrimp
1 serpent starfish
3 sexy shrimp
and assorted soft corals
I would also consider a heater with an external heat adjustment, you can stick the heater in the back area to make the tank look better too
Another cool thing about soft corals is many of them are aquacultured so you are saving the natural reefs.
3' fine sand bed 1x Orange Stripe Prawn shrimp goby, 1x sixline wrassemated pair of true percula clowns, 1x CBS shrimp, 2x peppermint shrimp, 1x pistol shrimp, 1x tiger tale cuke
, ~20+ snails, ~10+ hermits, 1xserpent star.
green Bubble coral, hammer coral (8 heads!) ,various Zoos,green finger leather, green star polpys ,shrooms
175w 10k MH
28w actinic 03
2x maxi jett 1200
Prizm skimmer (modded)
Hagen powerfilter(for running carbon 24/7)
nano arctica chiller