I'll give you an example of our bulgarian Renault forum. The first time I logged in was in 2011, when I got my first Renault, of course. First impression was shocking. It was a mess at first glance. At least 40 active topics every day (in the bad days). 200+ post for less than 8 hours. And everybody chatting bout everything. Mostly about Renault cars, but you could see even topics "What kind of milk should I buy for my cat". After a few days, I realized it's an entire society. Something like a huge family, with all it's quarrels, groups, good guys, bad guys, family affairs and so on. The first few months I thought, something is wrong here. It's a God damn car forum, why along with the car topics, should be so many unrelated stuff. Spending more time with these guys, made me feel part of this whole funfair and it was fun. Besides the guys were so united, they were making real life meetings every month at small groups and they have a nation-wide meeting every summer, gathering hundreds of them.
My point is - if you want a forum, that's alive and the members feel in it amongst friends, don't be too tidy
Let along unrelated material along with the car stuff. This proved working for 15 years in our case.