A further introduction into the various systems (i.e. trust, activity, merit, ranks) are relevant only after this.
I wouldn't mention things like trust, DT, the different type of flags, and things like that at all. That will just confuse newbies and maybe have them look for alternative sites to discuss bitcoin and crypto. For ordinary members, doing any changes with the default trust setup is something most never even do.
That's one of the things that should be linked to for further reading but it probably doesn't need to be given straight away. You could maybe give a warning about potential scams and how to look after your own money but the initial message should just include the most important rules as simply as possible so people don't get turned off by blocks of text and complicated rules, but people should be urged to read all the available links to rules/guides etc. If they don't then that's their fault.
May I suggest to what my idea is worth, a follow-through like a test/quiz/assessment for the new users.
Like navigation, and if they have at least comprehended the welcome message.
Making users pass a quiz and testing their knowledge might be too much. That is just giving them a reason to go away even before they started. Displaying a message with the most important rules and warnings why people get banned here should be enough.
I don't think people should have to take a test just to post here. It's just a message board at the end of the day and some people just want a quick question answered or whatever and shouldn't have to jump through hoops to do so so a quiz would probably be too off putting, especially to the average user and theymos is unlikely to do it. The answers to pass would just show up on a google search anyway and people would just google for them if they got stuck.
I mentioned somewhere that there should be links to the translated rules/guides as well.
That is not hard to get. You will find many members from the local communities who will help with that. Many local boards already have the rules translated in their boards. Compiling all those links in one post isn't hard. The only question is, will that ever be used or is the person doing that just wasting his time? We have been talking about the welcome message for years now and we still are.
Well only theymos (and maybe cyrus) can do that, but it should be made a priority and it looks like it's something most people want. It shouldn't be too difficult to include it in the current sign up process.