Ah yes, sorry for the metric measurements, I'm UK based! Thank you for the testing recommendation, I'll check them out.Glad to hear the tank was cycled and the LFS required a sample before selling fish!
Your tank is approx. 21 Gallons and roughly 23"L x 12"W x 18"H for those of us in the U.S. I'll let others make some stocking recommendations for you.
I like the API Master Test kit which includes the ammonia, nitrite, nitrate and low/high pH test vials and reagents.