56l isn't going to be big enogh for Discus or angels I'm afraid

They both get up to 8 inches in length and about 1 foot of height on them. There probibly wouldn't be enough space for them to streach their fins, let alone swim properly
Guppies are great little fish, though not very hardy.

I would wait untill the tank is 6 months old before getting any. They breed like the aquatic equivilant of a rabbit colonie, so be prepaired for 30 fry PER month PER female, or alternatively get all males

The females can have 4 broods of youngh from one fertilisation, and you need the females outnumbering the males 2:1, to avoid the females being harrased for sex to a point where they die. My male guppies were regularly seen trying to breed with other species, and though it was extreamly funny, it can get very tiresome for the other fish involved
There is a nice pinned thread for fish suited to a 10 gallon tank, and this is roughly what yours holds. Read through there and you will find many fish suited to your set-up.
Before adding any fish, you need to fishless cycle
with ammonia. Most LFS's will get you to cycle with fish, and this will caurse them serious long-term dammage
if they are lucky enough to survive

Please do the humane thing and go fishless. There is a pinned thread at the top of this sub-forum telling you how to do this

to TFF, and all the best
Rabbut