Hey Mike...  Welcome back!  DNN is still the same great platform and framework it's always been, but with a lot of contemporary updates and enhancements since version 4.  

You can still develop modules the same way as you did then, but there are more module templates available to you to make getting started a bit easier.  Probably the most popular one is maintained by Chris Hammond, but it requires Visual Studio 2012.  

https://christoctemplate.codeplex.com/ (though it's best installed through Visual Studio itself)

If you can't start from a VS project template, it's still a viable option to open the source version of an existing module and change that one to be your own.

Since DNN has always had a policy of being backwards compatible, all of your prior experience developing extensions is still relevant.  The only major thing that has changed is that manifest files have changed a bit since version 5.x.

Aside from manifest files, you have a ton of new capabilities available to you that make development even faster than and better looking before with minimal effort, including form patterns, DAL2, services framework, and more.

As you want to become more and more productive with your development, I'd suggest the following stream of learning:

1. Keep a constant eye on the community wiki and community blog for news about the API and framework overall
2. Follow the Module Development series of videos
3. Read through each of the "quick start guides" in the wiki for each recent version of DNN to know what's new to you
4. Join a DNN user group if there is one in your area (or start a user group if there isn't)
5. Consider purchasing the online training subscription 

As far as resources, it looks like you found the right place for asking questions and such.

My pleasure.  Glad to have you back in the community.  By the way, there's also a DNNCon event in October.  There is a day of training on Oct 18 and a free one-day conference on Oct 19.  You should check it out and bring some co-workers or friends.  :)