Partial replacement of wiring in the apartment: electrical panel diagram and cable selection

Michael asks:

Good time of the day! Petersburg, a house of pre-revolutionary construction (1914), gas, wiring in the interfloor riser Al with a cross-section (I will not say exactly), but I think 4mm2. In the dashboard on the staircase - AB for 20A. In theory, therefore, 4400-4600 watts are issued for an apartment - max can be consumed for an hour before turning off 6380 - 6670 watts.

Question 1: how to convert amperes to watts (multiplication) by 220 or 230
It is planned to make a partial replacement of aluminum wiring in the apartment, namely:
forward 2-3 copper lines of 2.5 mm2 to energy-intensive consumers, and leave the light and other sockets on the old aluminum wiring. The replacement of the lead-in cable to the apartment is not yet planned (we are waiting for the replacement of the meter by the Energy Supply Organization, and not on our own, it seems like from July 2020 this is their task and duty)

Question 2: is it enough to use 4mm2 copper wire in the manufacture of the shield, taking into account that in the future there will be a replacement of the lead at the input by 4mm2

Question 3: Are the current characteristics selected correctly:
• AB 20A (on the stairs) of IEK firm (currently standing)
• lead-in cable old Al 3-4mm (without replacement)
• counter (counter without replacing the old 1960gv)
• 2P switch for 25A (to turn off the power in the apartment)
• AB 2P - 20A (redundant)
• AB 16A groups for connecting new lines
• connection of old Al wiring (via terminals with connection to AB 16A)

I know about the installation of UFO, WPPT - but in this case, so far without them.

Regards, Mikhail