I don't know what the interface to your electricity meter will be like, but everything else you're doing seems fairly straight forward. I doubt that program space will be a problem. RAM is a separate issue, and you would need to know how much RAM your Nano variant has and what data structures your sketch will need in order to estimate the RAM requirements.
Given a project of this complexity it would be sensible to implement it in small steps, adding functionality as you go. With that approach you can be confident that the early versions will fit in the available program and RAM space, and measure how much they're actually using as the sketch evolves to see whether you're approaching a problem.
I suggest that the best way to get help is to only post when you have a specific problem or question that you want help with, and provide as much detail as is necessary to understand that problem or question. Anything involving software will almost always involve posting your whole sketch, but you can help a lot by doing some work in advance to reproduce the problem or question in isolation in a much smaller and simpler sketch. This will help your own understanding of the problem too, and quite likely you'll find that the act of reproducing the problem in a minimal environment reveals a false assumption or mistake in your understanding which enables you to solve the problem on your own.