CodeIgniter is very flexible and not as strict when it comes to implementing your own code and (libraries/classes/plugins). It's very simple, implements great separation (in regard of its MVC archt.) which makes it easy to understand and use. The framework has great, easy to follow documentation with great forum support and a growing community.
i say just watch one of their video tutorials of their website and you'll see how easy it is to get started on a project.
As for an IDE editor:
if you're using windows....i HIGHLY RECOMMEND PhpED (by nusphere)
I have tested every possible editor out there and this one by far is the BEST. It's fully featured in every aspect, easily customized and runs fast!.
they have definitely taken programmers needs and dumped it into this application.
it's definitely worth a try at least.
just checkout the features here.