Welcome to the Last War!
Congratulations on buying Ogre, arguably the best war-game made for over 40 years! Back in 2012 there was a monstrous Kickstarter campaign, where Ogre Designer's Edition was forged. This was the most comprehensive set of rules, units, Ogres and game pieces ever designed for the game. Although these sets have long sold out, Ogre Sixth Edition proudly carries on the Ogre line.
Despite missing out on the ODE Kickstarter, you can get virtually everything you "missed" through currently available options. First, I recommend you read this article, "Closing the Gap":
It describes how to bring Ogre Sixth Edition virtually on par with the original Ogre Designer's Edition. Some additional links include the following:
Ogre Sixth Edition - http://www.sjgames.com/ogre/products/ogre6e/ (presumably you have that!)
Ogre Reinforcements - http://www.sjgames.com/ogre/products/ogrereinforcements/
Giant Battlefield Map set - http://www.sjgames.com/ogre/products/battlefield/
Sponsored Counter Sheets - http://www.sjgames.com/ogre/sponsored-counters/
Don't forget the free Ogre Stream Overlays pdf - http://www.sjgames.com/ogre/products/streams/
Finally, there are a number of Scenario Books that are available to everyone as pdfs through W23:
Book 1 - http://www.sjgames.com/ogre/scenariobooks/
Book 2 - http://www.sjgames.com/ogre/scenariobook2/
Book 3 - http://www.sjgames.com/ogre/scenariobook3/
There is a lot of other Ogre material on W23 as well which should include the imminent release of Ogre Miniatures Set 1. The Kickstarter for Ogre Miniatures Set 2 is in two weeks . . .
If you haven't already, sign up for "Ogre News". That way, you won't miss a thing re: Ogre going forward. You can find the subscription link here: http://www.sjgames.com/ogre/
Welcome to the battlefield!
These are the kind of posts that make BGG such a valuable resource for all levels of experience.