Developing a Large-Scale Application in CI

[eluser]oddman[/eluser]
Hello everyone!

I am currently in the process of developing a browser-based game (not flash). I haven't been using CI long but what I have found is that it sacrifices development time for performance (and this is what we're after for the project, so it's a good thing!). There are a couple of things while I've been working with it that have raised questions as to how I would do it, or how best to implement. This topic is about one of those questions.

Basically I'm looking to use CI as the middle-man - getting the data/output it needs, processing input, then showing the display to the user. As part of this browser-based game, there is going to be a fairly large library that sits in the background that I want CI to be communicating with.

There's a couple of things I want to know:

1. Are there any shortcomings in using this approach from a software design viewpoint?
2. How hard is it to use CI's model system in order to retrieve data from outside of CI?
3. Is it possible to put a layer inbetween the controller and the model?
4. How hard would it to be to introduce a request-type layer. For example, if I send a json/ajax request from the view via a javascript layer, would it be difficult to have the application controller check the request then modify the output depending on the request?

I have some other questions but these are the most pressing.