It's more than just establishing editorial excellence and a publishing process. There's more to it than resourcing and talent. And you're living in cloud cuckoo land if you think it's all about tone of voice.
Of course, all these things are important. But content is digital and digital is big. Really big. So here's my list of things you need to consider on top of all those things:
I cannot say this enough, build a content strategy. Some will say it's the digital strategy (maybe) others will say it's the marketing strategy (no) and a small voice may want it in PR (again, no). Wherever you put it, make sure it's there and it's good or it'll become like the wild west.
You can't write a strategy without understanding what's already there and what's performing.
And a website can get out of control with constant publishing to plug SEO gaps, keep a track of what you're putting out there and every so often, run an analytics report to see traffic or through Web Master tools to check it's still ticketyboo.
It's also good practise to document what's on these pages and what may periodically need updating or removing , like offers, legislation, images, etc.
This is essential, not only to make your content searchable - both internally and externally - but also to deliver against a content strategy. And...
Don't publish everything willy-nilly, have a strict set of taxonomy and strategy that all content must adhere to if it wants to see the light of day on your website.
This might sound weird (and yes, I always have to think before I say this word too), but because across one website the same content may appear several times, it is essential you have a central depository where all this content is kept. This ensure consistency and if you change it once, you change it everywhere - even in the dark corners you've forgotten about.
Even better, it's all automated, but this is highly unusual, even for the slickest organisations.
Along with your strategy, this is really important. How will you ensure content adheres to your lovely strategy and that everything publish is of a high standard.
So, by all means, write a tone of voice and put together style guide, but content is a lot more than that.