Firstly, congrats and good luck on the resolution! I'm a guitar player too, but by no means an expert
It's really good that you've started with a previous instrument, which I didn't! I would say start with practicing chord positions of course, and once you've memorized where which chords are, practice switching from one chord to another. Try looking up some pentatonic scales, too. Those helped me a lot.
Also, since you're a piano player, I would assume you know how to read music. While that's really useful, I would suggest learning how to read tablature or "tabs". It's a very handy way to learn how to play a song quickly, and is the format you'll mostly see when looking up how to play songs on websites like
ultimate-guitar.com <They have a BIG selection of songs. Here's a how to on reading tabs:
link
As for Zelda songs, I just got into playing them, and they're addicting! Some of the ones I find easier are Epona's Song, Requiem of Spirit, Song of Time, and parts of the Lakeside Laboratory. Some of the ones that I'm still working on is Bolero of Fire and Song of Storms. Here's a really awesome website that has the guitar tabs for a TON of video game music, including a heaping bunch of Zelda tunes:
http://www.gametabs.net/series/203 Enjoy!