- Single phase using 2 wires
- 3 phase using 4 wires (Red, Yellow Blue, + Return)
If you don't indent to run 3 Phased equipments (e.g. 4HP a/c, 5KVA Oven ), all equipments are running on 240v only.

and

The house have the wall socket run independent without looping, And all high load (e.g. WH, AC, OVEN) points are independent (direct to MCB without looping). Than technically you can just pull in the 4 new wires, distribute the load on other phase.

Or maybe you have another DB box on 1st floor, use one phase for first floor DB, ground floor share out the 2 phase between load.

Yes, but i think anything above 10KVA (about 45 amps) is better to go with 3 phase provided your house wiring support it.

If you have a looping socket, max it take is 15 amps in total. Don't overload else you risk of catching fire.

Wow, now many double story house owner so well to do. Can take up load of 40Amps.