New property - looking for help understanding the heating system

Hello!

I've just moved in to a new property with "all electric" heating system and trying to figure it out. The agency/landlord are of no help so trying here. Previously only lived in properties with the usual gas combi boilers so a bit lost. It's a one bedroom flat with two of us living here since a week ago.

Questions:
1. There are two separate electrical meters {#2 and #4) - does this mean I need a contract with two separate companies? It seems it should be SSE for 'normal' electricity and Veolia for the boiler one but not sure if that's logical.
2. I've tested that both hot water and radiator heating works ok via the control panel in 1.1 photo (still need to figure out how to program it) while the separate "Immersion" button was off. What is the purpose of that "Immersion" button then? Though it's an on/off for the whole system but doesn't seem to be the case.
3. What's the most financially sound way of using the setup that I have both for water and radiators? Set a preset schedule for the water heating for e.g. 2h a day and keep the radiators always on while adjusting the thermostat in #5 as needed?

Seriously appreciate any information, tips and advise the pros on this forum can provide!

I would hazard a guess that this is in a block of flats.
The meter in picture 2 is your electric meter and I suspect the meter in picture 4 is metering the heat energy used from a centrally supplied source of heat.

This would usually be a large boiler, heat pump or something like that which provides heated water (or other heat exchange fluid) to each flat, inside the white box with the meter will be a heat exchanger which transfers heat from the central system to the internal system in the flat. The meter in the box records how much heat energy you have used.

I don't know how the billing of this normally works but I woukd expect it will be billed by the management company for the building.

The immersion heater is there as a backup option to heat the hot water if the normal source of heat is not available.