Hi Emelie, welcome to the forum 
The Rio 125 is a nice starter tank - I used to have one till I upgraded to 180 litres.
Do you know how hard your water is? In the UK, our water suppliers' websites usually have that information but I don't know about Swedish water companies. It would be worth checking to see. The hardness of your water will affect the fish you can keep.
Have you read about fishless cycling yet? There is a thread on how to do this here
And finally, one of the best resources for information on the differing species of fish is Seriously Fish. This site has information on the water requirements, tank size and compatibility with other species.
Hi Sue,
thank you!
Yes, I'm very pleased with it this far. Looks so much bigger than I had thought, in a good way of course, and very pleasing and well fitted in my flat.
I do, yes. The water is soft, bordering on medium hard during the summer. Up until know I've just checked all the fish that I could be interested in, going to filter through it looking at parameters such as water hardness and temp now.
Yes, although I'm running it after what my local fish store said to me. They said that buying testing kits and such wasn't necessary at the moment and that it was just fine for me just letting it run whilst adding Easystart (bacterial combs system) from Easylife once a week for 3 weeks.
Oh, another site - that's great. I'm going to take a look at that one as well. I've used Think fish's information and a Swedish fish guide site, but the more the better. Also, I just love doing research so, the more material I can shift through, the happier I get, haha.