See this MSO post for some more information on this decision. You're welcome to raise the issue of allowing image links like this, but since there's an easy and better way, I doubt any action will be taken.

Ideally, you should be using SU's image upload functionality. That way, you won't break the post when the images get removed from your own server.

Well, the about page may be a worthwhile substitute, and IIRC it's quite prominently displayed at the top of the page when you aren't logged in. But it's difficult to find a way to make it more obvious without getting in the way - again, User Experience may be a good place to ask.

Unfortunately, the current design of the help centre is such that is is infeasible to force someone to go through the whole thing. In any case, forcing someone to read instructions (how would you even verify that?), as good as that may sound to established users, is a great way to drive, well, almost everyone away. You might want to consult User Experience on that.

@michel-slm Nothing too unusual about that. Likely two different data sources. Anyone who viewed any of your questions would see the badge count (which would also have a longer cache expiry, since it's served more often). When you view the badge list explicitly, that could be uncached (not viewed often enough to matter) or not have been accessed recently, leading to the first load of the cache with fresh data.

Another important thing to consider is there is often overlap between SE sites - the same question might

Yup, SE's main site is more accurate, and Data Explorer should only be used for general statistics. I've also updated my answer with a SE API query that should be real-time (minus some caching), just in case anyone actually needs this information in a more script-friendly format.