Hi Mike-

Happy Holidays and congratulations on your new guitar!

I've taught many adult beginners, some of whom are on the bigger side. For the most part, they do just fine after a while of careful practicing.

Occasionally, for certain chords like an A major, you may have to find a workaround if you are not able to make it the traditional way, which is having three fingers next to one another all in the third fret.

In my opinion, the best thing you can do to set yourself up for the best results is to make sure your hands are approaching the neck at the correct angle, and that you develop enough finger flexibility and coordination to make the tiny little adjustments that will make the difference for you between good clear tone, and compromised tone.

You may wish to try some of the Spider Legs series of warm-up exercises to get those particular skills up to snuff. Here's a link:
http://www.guitartricks.com/tutorial.php?input=621

Good luck, have fun, and keep us posted.
Best wishes, Lisa