For your first and third points, I think the forum already does that. As scriptninja already mentioned, the Latest view should show you the latest posts regardless of category. There does seem to be an edge-case bug though, where the ordering of some posts can be wrong, but that should happen only rarely.
For you second point, I've looked into it and it appears to be a limitation of the software platform, to only display "excerpts" for the the original post. I agree though, it'd be nice and more useful to see excerpts of the latest post. I'll see about putting in a feature request for that or even consider if that's something I can develop myself, if/when I can find the time.