As for what i know that 220-240v 40a are 3 wires plug and cable, which are 2 hot wire and 1 ground wire. Each hot wire are still only 20a.
15a or 20a are normal outlet in most home in the US, which can hanle 1800/2400w. I will reserve 20% of the load for safety due to if you are running the power consistently over 3 hours. so you are talking about 1440/1920w per a breaker line (not each outlet).
With your kitchen 240v that really don't give you much if you running a 6-8gpu rig 1k-1.2kw. which only allow you run 2 rigs or 3 max. BTW most American home power line are 100a cable from outside, apartment that depend could be 100 or 200a. you really can't setup like mining farm, because you will max out your power line after 4 rigs that take 1kw+ each system. Unless you not using any electricity at home, like Microwave, AC, Ranger, Fridge bla bla bla that draw power as well.
It depends.
NEMA 6 uses 2 hots and a ground for wiring to devices that are 234 volt only.
NEMA 14 uses 2 hots, a neutral, and a ground for wiring to devices that use BOTH 234 volt AND 117 volt - most commonly electric ranges/ovens as the clocks normally are standard 117 volt clocks while the heater elements run from 234 volts.
Home outlets NORMALLY are NEMA 5-15, 117 VAC 15 amp - 20 amp outlets at 117 VAC are UNcommon, but do see some use for high-power A/C units and occasionally in shops/garages.
It is NOT uncommon to see a 20 amp CIRCUIT in a kitchen, with a pair of 15 amp duplex outlets on the one circuit.
Most US power feeds on NEW homes are 150 or 200 amp - 200 in areas of cheap electricity, 150 where electric is not cheap but natural gas is available.
Apartments are commonly 50 amp in natural gas heat areas, 80 or 100 in cheap electric areas - but even THERE I've seen some 50 amp apartment feeds in the area I live in which is VERY VERY cheap electric and can't GET natural gas at all.
I've NEVER seen an apartment with more than a 100 amp feed, though I won't say that they don't exist in very high-scale high-end apartment buildings.
Before you start pulling large amounts of power, though, DEFINITELY CHECK how much you have available - which will normally be what the main breaker on your main panel is rated at (if it's NOT then the breaker was mis-installed or someone unqualified changed it, that matchup is a NEC reguirement).