Oleg, I will say right away, do everything with your usual ease, like a child. Give yourself up to the process entirely and forget about the result.
The surface depends on the situation, let the case decide.
What about the paint:
A light can for underpainting, saturated colour for the primary fill with the addition of finishing spray cans, black enamel for outline (with a brush).
Put the enamel juicy so that everything fucking flows.
You can add a cross
After completing the process, document it or do not, leave the paints at the work. Let the city decide for itself - is ok or not ok?