[eluser]Jelmer[/eluser]
It's a bit of a strange question I think. Could you make all that with CodeIgniter? The short answer is yes. However, to me, CodeIgniter is like a toolbox - one could conceivably make anything with the tools, it's one's own skill and imagination that limits the scope of what can be done.
So the longer answer is probably that CodeIgniter gives you the tools to built all of that within CodeIgniter's generous MVC structure. But it doesn't come with an overblown number of libraries, it's not a plug-and-play repository of bits of application you can slap together to create your own blend. That being said, when you take a look in the wiki and forums you will find lots of other users' contributions that will either help you along or even give you exactly what you need.
To you last point specificly I'd say there isn't any problem using either TinyMCE or any Ajax library. I'm using TinyMCE a lot and after having tried MooTools and jQuery I've settled for Prototype/Script.aculo.us for any Ajax/JS stuff I need (not directly a recommendation, I just liked these better - you'll find many fans of the other 2 here as well). I had to learn a lot when working with these libraries, and CI made my life easier - and I believe that's the bottom line of a good toolbox.
