I think it's hard to get any real sense of what he's like, because (assuming Raynor is the one solely responsible for the three books) we never get to see him other than presented through a Vaseline-y soft-focus glow of hero worship.
You get glimpses of him as a free-spirited, outdoorsy, blond-plaited 20 year old with eccentric dress sense (am still hoping that a photo of him in the bright cream-coloured suit in which he got married will surface somewhere), but on the rare occasions he engages with people other than Raynor in TSP, he seems more the tiresome, can't-shut-him-up 'raconteur to captive audiences' type:
But he always could tell a good story. He’d told stories in builders’ snap cabins, in queues for the bus, to children on his garden tours, to the visitors in our barn, to anyone who sat still for too long. Captivating people with his tales of everything from history to botany. [...] He’s always had such a loud voice, never one to whisper.
I note that immediately after this comment (which is from when he starts reading Beolwulf in St Ives), Raynor actually acknowledges that 'savvy' people in town for an arts festival are not his usual 'captive audience'.
But on the other hand, he seems to have completely captivated Jason Isaacs, even if we give some leeway for luvvie-ish exaggeration.
But yes, I don't think he has had anything like a 'career trajectory'. Casual jobs in construction, or jobs he talked his way into.