Those are good questions and I don't have all the answers. We moved to Octopus from British Gas years ago. They provide good tariffs if you have an EV and/or solar. Over hthe winter I charge my battery on cheap rate and that can run the house all day, so it is worth it. The battery is not huge and can be outdoors, as ours is with a small shed over it.

Most EV chargers can have a schedule set or you can do it on the car itself. You can also add timers on appliances. I keep meaning to look again at Home Assistant to give me more control options. There are lots of automation options these days. We tried to automate some things when we built our house over 20 years ago, but things have moved on a lot.

I would hope that the plug-in solutions will get cheaper. I am not sure if you can just buy the inverter and add whatever panels you can find. The panels can be quite big so you need to consider where you can mount them.