Electricity isn't just expensive

[nzoomed]

OK, I was looking at roughly doube the capacity (~7kW for the home and another 7kW to charge the EV) I probably dont need the extra power unless I was using that load while charging the vehicle, but if I already have a battery bank, I could just use that  power anyway to minimize taking power off the grid.
Would also mean I would need to charge during the day to maximise the savings?

You're best to calculate your home's electricity consumption as this will be a deciding factor in how much PV generation you can consume instantaneously, which is where the real value of PV lies. Our inverter provides us with real time generation and consumption data. e.g.

As you can see our 'background' consumption is around 0.5kW and for us that relates to lighting (LED), two 700L chest freezers, 2 fridges, a heated towel rail and a few appliances on standby. The consumption peak that evening was probably oven use.

The morning consumption (in yellow) was our diverter heating the HWC, and the afternoon was our Evnex EV charger charging our EV. Both these units monitor export to the grid and tailor their consumption to suit (avoiding drawing from the grid). And yes, having an EV at home during daylight generating periods is key to matching their charging to your otherwise exported electricity. Most EVs have batteries larger than 50kWh and to discharge a home battery for EV charging is bad economics. It will prematurely degrade the home battery and most home batteries are in the 10-15kWh size. The price of 50+kWh of home battery is close to that of an EV, hence why I'm holding out for V2G.

We have recently changed to Octopus as our supplier whose off peak rate of 18c/kWh which is so similar to the 17c export rate they pay us that it makes very little sense to be charging a home battery as the only time we would gain from drawing down on the battery would be the dawn and evening peak periods. The payback on a battery would be so extremely long that it's not worth considering.

I know people who are using banks of 18650 or 21700 cells in home made battery banks that work well, bit of work assembling them, but if can be cost effective, there is a plentiful supply of the things from e-scooters, etc.
I dont think I would build myself a bank much bigger than 5kWh if I went down that path.
Im definitely doing alot of research on the subject, I have a friend who has also learned a great deal, so any mistakes he made, I will be aware of. There are probably some things I would do different to him already, notably around the batteries used, but he got a one off good deal on the components. He is assembling his battery bank and installing the BMS himself, he is using CATL cells, but I have learned that the EVE cells are actually better and have less issues with them swelling up and the need for clamping properly compared to CATL.
I think I would be best to charge an EV during daylight hours and use off peak hours the rest of the time.