Any one else using it?

DNN newbie question alert

I'm in the process of taking over a project from a developer that's leaving and I'm looking to fix some things in this app and looking for the correct place to do it.

1) I need to find the correct place and way to implement some common code that all of the modules can use. Currently several modules all use their own copies dbutils.cs.. with some chance that individual module developers tweaked their copy of the code once they got hold of it.

2) I need to find a way to create custom custom UI controls that can again be reused across modules. The original development team each developed their own client selection combobox rather than using an app wide class.

So can someone give me some pointers and/or point me at references to get this project back under decent control?