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I have a similar background, and just recently started again. I started out with some more basic songs.
There are tons of theories out there on practicing and playing. Hanon is good to get your fingers trained again, but musically it's not as much fun.
I would suggest finding some easier pieces and work on playing those well. That way you can build up your confidence, enjoy yourself, and work your way up to trickier compositions.

Personally I started with 'first lessons in Bach':
https://www.amazon.com/gp/product/1423421922/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

And album for the young by Schumann. These pieces are really fun and quite varied as well:
https://www.amazon.com/gp/product/0793529948/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

Then for some great advice which I picked up on the pianoworld forums:

• Don't try to rush through a song and make the same mistakes every time. This way you're training yourself to play the wrong notes, and it becomes harder each time to unlearn it.
  
• Instead, start playing very slow and make sure to get the fingers and notes correct from the beginning. Once you play it right at the slow tempo, start playing faster.
  
• Instead of playing through a piece from beginning to end and glossing over the few hard sections, mark those... and then practice them until they're easy. Break down in very small sections and practice until you get it right!
  
  This has really proven beneficial for me, and allowed me to learn pieces quicker! Currently I'm working on Schubert Impromptu Op 90 No 3. It's so beautiful.
  Good luck in your learning. You'll most likely get frustrated, which is normal. Learning the piano is a marathon, not a sprint. There will be days where you can't hit a right note, but other days where you surprise yourself.

Many years since I read it, but I remember this book being insightful: https://www.amazon.com/Piano-Works-Claude-Debussy-Dover/dp/0486215679/ref=sr_1_3?s=books&ie=UTF8&qid=1468531153&sr=1-3&keywords=debussy+piano+dover