Brick house stands on a concrete slab, then 40 cm of sand – EPS 10 cm-monolithic floor. Need to level this floor with differences max 10 cm on 140 square meters of the first floor.
Most of it without a warm floor, part of the wiring pipes with a coolant in special mats with a heater already. Two types of coating – porcelain tiles, where the pipes and parquet / board where there is no floor heating. The floor is also laid on the heating pipes in the insulation.
I think that the right thing to pour concrete m300 with a small fraction of crushed stone, but do I need to put insulation in general? Do I need a primer? Do I need a grid?
Insulation is never superfluous, but everything must be in moderation. You already have 10 cm, but it's not enough. At least 15 cm thick you need.
If you are going to insulate, you should always screed with a mesh.
If you are going to pour concrete on concrete, you need to prime the bottom layer so it does not take moisture from the top (grid in this case is not mandatory, but it is advisable to add fiber).