I'll second the ATI recommendation. Here's the link: Home
Dave Stohr has tons of real world experience as does Mitch Launius. Mitch has done ADS-C/CPDLC crossings himself and is very up to date with all the latest changes to oceanic and international ops.

They'll come to you or you can go there.They also have a big library of info as well as lots of recorded webinars you can access online.