New to CI

[eluser]Michael Wales[/eluser]
Your understanding of the MVC concept is spot on - you could even take it a bit further by extending the validation class with an if_exists() function or working on some code to move validations into the model, or completely new files (my personal preference) called validators. All of these are advanced options and things to look at down the road - I would stick to the basics for now, which it seems like you have a firm grasp of.

As for the way CI handles sessions - there are quite a few session libraries out there, all of them really great. I highly recommend you look at DBSession, sounds like what you need - of course, you could always write your own library as well. Nothing wrong with that at all.