If you have the eight edition codex, you're good to go. Army building hasn't changed since the beginning of eight edition as well, so whatever you've been doing before, will work now.
There has been some points changes in Chapter Approved, and some faq/errata changes, so I'd check all that stuff out. But, chapter approved came out a year ago, so it probably came out before your hiatus.
There was a big faq/errata release in September, so I'd give that a peruse. You can find all that on the community page. FAQs - Warhammer Community
Have fun getting back into the game! The one thing which might have come out while you were away, was the new game Kill Team, which makes for fun small scale games, with a campaign system built in.