Ok. So I've put everything back together and, lo and behold, it's started. Unbelievable!!!
First of all, I must express my appreciation to all who answered the post. You've done quite a lot.
So I've cleaned the exhaust breather compartment (it was full of gank), changed the evaporative valve.
Changed intake manifold and rocker cover gaskets, bushes, cleaned the throttle body. Cleaned a fuel rail, changed a fuel pressure valve. Also I've changed spark plugs (put ngk tr5a gap 1.0 resistance 5kOhm), spark plug wires (I've chosen autolite as magnetti marelli have turned out to be of poor quality - too thin with fluctuating resistance).
I cannot definitely say what was the cause. But from what I saw, the intake manifold gasket had been sealed to the extent that the sealant was restricting a passage of exhaust air from entering cylinders' space. Also there is an air box resonator missing (don't know how it affects the flow).
Now (apart from steam, which is coming up from the exhaust manifold) the car runs much prettier. No misfiring, no stalling. Beautiful.
The next step would be to read codes from ecu.
Thanks to all