@DarkSheepArts Linking to an accessible companion guide on a site might be a better shout than braille. That would be easier to produce, easier to update, definitely cheaper to maintain and most importantly, it places the choice of how to consume that with each person who wants to read it. EG, I'm totally blind here, learned braille so young that I can't even remember not knowing it, but there are boatloads of blind/VI folk who lose sight later in life and never get that opportunity. IMO audio is a really nice to have extra if you can get it done within budget, but deafblind folk get the soggy end of the stick so often, I reckon I'd try to offset that a bit by commissioning a good writer over a sound designer if I were in your shoes.
BTW I live in London and my partner bloody loves a museum/exhibit. Would be happy to come and poke around ideas in progress. Holler whenever you've got something if that might help.