Porting ExpressionEngine to CI

[eluser]zdknudsen[/eluser]
Okay so I needed a system similar to ExpressionEngine, when making sites for clients.

Currently I'm developing a community-driven website and I would like to use a CMS.

But since I do not need that many of EE's features and I had some additional needs I thought I would make it with CodeIgniter instead. Now I have a few questions regarding a port of EE to CI.

Am I allowed to create a templating system that parses like EE? (Modules = classes that can be used on templates, and modules similar to that of EE).

Can I use EE's database structure?

And basicly to what extend one can copy EE's features, seeing as EE is a commercial system.