Long-term Berliner here
I agree that it's crucial to determine where in Germany your character comes from - not just Berlin or Bavaria, urban or rural, but also East or West. Even 30 years after the Wende, some people in the East can be lacking in self-confidence by comparison. I find a lot of West German men frankly arrogant as hell.
Lots of social attitudes and expectations get drilled into young kids here, at nursery at the latest.
- Environmental awareness - that starts with always turning off the water while brushing your teeth (my 4yo daughter started telling us off by saying 'Wasserverschwendung!' whenever she caught us, and she learned that from nursery). Not caring about environmental matters is literally viewed as a sin.
- Wrapping up warmly as protection against the weather, and dressing practically being more important than fashion. That's important - it's cold here in winter. People will have learned it from their grandparents, for whom it will have been literally life or death.
- No real embarrassment about the body. I've been naked in saunas after climbing when the only other people there were male strangers. It's really not a problem because there is no erotic element, and your climbing character wouldn't see it as a problem either. Au contraire, he would find it utterly bewildering and disgusting that people wear costumes in the sauna in the UK. Filthy habit!
- Certain things are just not done or tolerated. Children are not allowed to put the soles of their shoes on seats, and that carries over to adulthood. When you go into a doctor's surgery you're supposed to say 'good day' to everyone waiting (I still find that excruciatingly embarrassing).
I find German men in particular are obsessed with not losing face or being shown up. It leads to a lot of mansplaining (but they mansplain each other too). If a German man wants to take up a new hobby he will research everything possible about it, then go to the best specialist shop in town and ask the salesperson countless detailed questions, then buy a whole pile of really top-notch gear. When German guys do something, they have to do it really well.
Your man will be (or will have been) a member of the Deutscher Alpen Verein, and their free magazine is called Panorama.
Someone mentioned he would go to Decathlon for climbing gear in Berlin. It's more complex than that, because it depends what he wants to boast about afterwards. If he wants to show off about the bargainous price he got for gear that's just as good as the expensive stuff, he'll be in Decathlon. But if he wants to show off his insider knowledge, and have a huge discussion with the knowledgeable sales assistant (who will also be a climber, so they can have a boasty pissing contest) then in Berlin he's more likely to be in der Aussteiger, Mont K or Globetrotter. And frankly, Decathlon is a bit downmarket for an image-conscious climber.
Germans have an insurance policy for everything - you could get some fun out of that. Health insurance, house insurance, personal liability, legal, broken glass, sickness... Your man would be frankly incredulous that a Brit doesn't have personal liability insurance.
Ultimately a lot of this is about the image that German men want to project of themselves (cool, a bit wild and rebellious, in control, knowledgeable, nature fan, uses the 'Du' form to everyone whether they like it or not) versus the reality (loves a bargain, likes security, prepared to go Sunday shopping as much as the rest of us if the shops are open, plans things in every detail).