Just want to say, first off, that the current size of those fish (the cories and danios etc) doesn't matter. You need to look at adult sizes. The albino cories will get to just about over 2" and the danios to just under 1.5" (none of this counting the tail BTW). Most people also don't include shrimp in calculations unless there's a lot of them. 2 ghost shrimp won't be adding much bio-load and certainly don't use up all that much oxygen.
Out of the fish you are considering, I'd forget about the indian glassfish and marbled hatchets. The hatchets because they occupy the same area as the danios (top of tank) and are also prone to being nipped and bullied and should be in a larger group than just 3 because they are shy. In a hexagonal tank the surface area isn't realy enough to offer the danios and hatchets each enough space in the upper layers. As for the indian glassfish, besides the fact that they are also rather shy fish and you'd probably not see them all that often anyway, they do better in water with some added salt (which cories can't tolerate) and need to be with very peaceful tankmates.
Which brings me to the serpae tetras. These are known nippers. Though they'd be fine with your current stock, I'd not mix them with guppies. If you want a livebearer, I'd go for the platies (1 male, 2 females or all the same sex).
The black phantom tetras, on the other hand, I highly reccomend. They are my favourite tetra because they actualy have character and what they lack in color they make up for in behaviour. Males display to each other spreading their fins and 'flaring'. They can rapidly change color so that you'll see them hovering one minute a silvery-white, the next a highlighted irridescent black. The females have shroter fins but have a bit of red which provides that extra bit of color and distinguishes them from the males. A large group of females looks fantastic. Phantoms are also peaceful and you'll soon get to know each as an individual. Besides, it isn't only colors that provide interest in a fish tank, the lateraly compressed body shape of these tetras also add contrast against torpedo-shaped danios and, if you still want color, a closely related species - aptly named the 'red phantom tetra' - looks like a red version of your typical phantom and is equaly endeering.
So, anyway, IMO, you are about half stocked right now. A group of 6 black phantom tetras and a trio of platies would just about do as additions. Maybe you can add some sort of 'centerpiece' fish later on (once the tank is 'mature' in about 6 months time) but keep in mind that it's a hexagonal tank so you should aim to understock compared to what you'd put in a typical rectangular aquarium.
