FS was that nice and made a drawing, see Optical cable and SFP advice - MikroTik
I'm still a bit puzzled why do I need when I have only a single point to point connection
That's a set of 1000BASE-BX10-U(plink) & -D(ownlink) optics respectively which you need to drive the simplex fiber path.
So one SFP has to type uplink and the other downlink, isn't it? But why, is there any explanation for this?
DOM support makes sense as well but what else di I need to take into account?
There are multiple SFP-GE-BX, only distance, wavelength and connector type changes. How do I choose the right wavelength?