Hey, Amy; don't be disheartened! 'Rather large'; aww bless! (I don't mean to sound patronising, btw. It's just the idea of a 55l tank being 'rather large'
is quite comical when you've just finished water changing a 5'x2'x2', as I have!)
As I said, it is a nice little tank, and you do have plenty of options with it, it just needs little more thought and planning than a larger tank would.
If you go onto your water supplier's website, it'll give you all the info you need concerning hardness; it can be really confusing, but you can always post here and someone will explain it!. All you really need to know for the moment is whether it's hard, soft or medium.
The kind of water you have affects your potential stocking, as soft water fish don't like water that's very hard, and hard water fish do really badly in soft water. It's quite difficult to change hardness, so it's better to pick fish that will be happy in your water, rather than trying to change it.
I'm afraid there is more to cycling a tank than just letting it run for a week. You really need to be adding a source of ammonia, especially if you've got some mature media in there, or the bacteria will starve to death
Having a look through the threads and articles in our 'Cycle your Tank' sub forum might be a good idea for you, as it goes into far more detail.
As to the rams....they're small, but feisty. If you wanted just one specimen fish. I suppose you could do a ram (although it depends on your water; as well as being feisty, they're incredibly picky about their water too), but in a tank of that size you would be very likely to have serious aggression problems if you wanted any other fish in there. My last ram killed nine neon tetras before I realised what was happening and removed her, and that was in a four foot/240l tank.
Also, you'll see a lot of very 'over the top' stocking suggestions, all over the internet. I will admit that, on this site at least, we do tend more to the more conservative side, but that's because the years of experience we've built up between us have demonstrated that fish are 'happier' (although that's a
very difficult thing to quantify!), show better colour, more natural behaviour, grow larger and live longer in appropriately sized tanks.
We also like to promote the very best possible practices in fishkeeping. Of course, in the long term, it is your tank, and you can put what you like in it; no-one's going to come around and remove fish from your tank! We do have a habit of saying 'told you so' when it all goes wrong, mind you (we're only human, after all!).
Anyway, find out what sort of water you have, read up on cycling, and then post back and we can help you move on from there. I'm sure your little tank is going to make you proud in the long run