I think in your position, I'd find a really good estate agent and tell them your requirements and budget and see what they come up with. I do think flats are moving slowly (or not at all), so that's in your favour. I think in your price bracket you can find something nice but you're probably going to have to compromise a bit somewhere - either on the size of the flat or the location.
I'm not in love with Maida Vale. I don't know why, but I find it a bit meh. We're in Notting Hill, which I love, but it would be a rare day that I'd walk to the west end - I've done it, but life doesn't really allow time for that all that often 😅.
One other suggestion is to not rule out taking a look at Queens Park. It's got a really nice high street these days, lots of restaurants, a great farmers' market, and the Bakerloo (straight into Marylebone, central, and Embankment for a quick walk across the bridge to the south bank) and the overground (Hampstead, Islington and East) are both super convenient. In our 20+ years in London we've lived in the heart of Chelsea, QP and Notting Hill, and I have to say that QP was my favourite in some ways. We have a car but could easily have done without it. I know it's not the same as a two block walk to the theatre, but it's worth a look.
Sounds like an exciting move. Let us know what you find!