If you want to express yourself, you need the services of a lover or a psychiatrist; if you want to express a book, you might conceivably manage it.
Being a writer usually entails a fairly quiet life. However much travel one might do, however many tours and appearances, the job entails solitude: long hours in libraries, long hours at a desk.
I honestly don't think Peter is that interesting without Harriet - the only exception being 'The Nine Tailors', which is such a good book it doesn't really matter whether he's got a consort or not.
I think that novels are tools of thought. They are moral philosophy with the theory left out, with just the examples of the moral situations left standing.
I worked for many years as a writer for children and then wrote two adult novels of the kind they call 'literary' without any very great disturbance to this kind of life. Then, something went wrong. My third adult novel was rejected by the publisher of the first two. And I could not understand the criticism offered.
My grandfather had a proper bookcase of egghead books, and he gave them to me in alphabetical order. So we moved from Aeschylus to the Brontas, and I can still remember the great relief of going from the dipus cycle to Jane Eyre.
There's no point in using someone else's characters if you're going to turn them into your own vision. You have to be loyal to that person's worldview and sensitive to what they would and wouldn't have done with their characters, and how explicit or inexplicit they would've been.
You can't deduce the personality of the potter from the pots. It's a thingy you've made and offered to somebody else for their use, and, believe me, a novel is like that. It's a made thing and ought not to contain a direct self-expression of the writer.