So would P(total) consider the gas's pressure only?There is no other pressure.
The pressure is P. P everywhere. P in the gas, P in the liquid, P on the wall. (That's not an instruction, by the way!)
Pressure is an intensive variable. It is the same at all points in a system at equilibrium. Just like temperature. If the temperature of the gas was T, and the temperature of the liquid was T, you wouldn't say that the "total" temperature was 2T, would you? [Note, this assumes your system is small enough for gravitational pressure to be neglected. It wouldn't be true at the bottom of the sea.]
What about the pressure exerted by the liquid on the walls?
What about it? It is, I repeat, not additional
to the pressure of the gas. Where the gas is in contact with the wall, the pressure is exerted by the gas; where the liquid is i contact, by the liquid, but the pressure is always P.
Lastly, after all the gas had been liquefied what pressure do we consider now?
As before, the pressure of the system. Only now there is no gas, we may refer to it as the pressure of the liquid.