IKEA Cylinder tank + advices

[Shrimp King]

Hi all,

Long post ahead so please, keep with me 

So, I have this unused IKEA Cylinder which I decided to turn to a mini-tank for an Amano Shrimp (planning just 1, 2 at last)
I did the math so it's about 5L (1.32 gallons)
My plan is to get:
1x branch
1 or more stones
5x Marimo balls (2-3 inch/4-5 cm)
1x Egeria densa for the background
1x plant for carpet/front

Now the questions are:
1) I have no way to get RO water so I have to rely on tap water; I live in Slovakia and it's said water is one of the best around in Europe, so can I rely on that?
I would wait at least 1 month before getting the Amano in it

2) Online shops have anything from the list above but decorative stones; is it ok to take some pebble from the street and put it in the aquarium?
I heard calcium may make the water poisonous

3) I am planning to use no filter, no air pumps, nothing; with those plants above and considering the size, and considering livestock is literally 1 or 2 Amanos, is it going to thrive anyway?

Thanks for your patience,
Andrea