I think what made the Ubuntu MATE community warm and friendly in the beginning is that we don't import the legacy way of how forums operate - like hard rules, "read this before posting", or encourage any kind of elitism or strict formality.
Discourse's FAQ uses the "public park" analogy. 
I think that works well. I feel introducing a support FAQ like this risks vibes like:
"Hey! Mint user! Get out of the park! UM only!"
"What?? Caja in Xubuntu? Get outta here!"
"PowerPC Mac!? Nobody uses that any more!"
"UM EOL? I don't care you need it for some old software! Upgrade anyway!"
... those kind of vibes just kill a community.
Instead, we could:
- Pin the site-wide FAQ to the left sidebar, by default.
- Add a section to that FAQ if we feel we need more emphasis on:
- Support detail - what went wrong, the system, what has been tried.
- We could mention our community consists of ordinary computer users from different industries & countries.
- We can edit the message when users write their very first topic.
- We can set up a template when users create topics in Support & Help Requests
- We could introduce profile fields, requiring everyone to fill out their primary system specs or OS choice. I suggested this before I was moderator but I don't recall it was successful then (as optional fields, anyway)
- ... also, there'll be many users who aren't very tech-savvy. What seems simple to us might be very complex to them.
- ... a good point was raised that people might have multiple systems.
Some other thoughts:
- Discourse works well as a place for long-term knowledge. Not as a dumping ground of quick questions that's been answered numerous times. If this place is a mess (e.g duplicates, low quality), we might need to start cleaning up.
- Sometimes, a web search lands users here... and we all know that feeling when results are utterly useless. So, deleting old, abandoned topics could be justified.
- If we were to go all-in "Ubuntu MATE exclusive", then we risk closing up and migrating to Ubuntu Discourse's "Ubuntu MATE" category. Just like Lubuntu did, because they'd be advantages being part of the wider Ubuntu community.
We do have a Leader role, if we need more hands on the tidying (editing titles, recategorisation). Regular users have some minor abilities too.
In the wild, I had something deleted from Discourse Meta because they were tidying up and my support request for an email problem didn't get resolved... That's an option should we wish to take that approach of "cleaning the park" to lead by example. 
Anyway, that's just my thoughts. I appreciate time was spent on this proposal. What are the reasons for wanting a new FAQ and can we improve what we already have?