I'm not sure what you plan on using this piece for, but if you want to have control over everything you're doing and want to finish within the next year, you'll have to size it down considerably.  Unless you feel like detailing an 800 pixel wide area of sand, ofcoure. 
Perhaps you could break it up in a few sections for yourself so you can sketch everything before you start with details?  Like a fore, mid and background, the sky and the character - much like in a video game, only with smoother transitions. I've never really done this sort of thing before though, so I'm not sure if it would help at all.
As for the moon, just look for some references. You'll probably want to avoid the spotlight sort of thing and just focus on the craters and how it's going to be a source of light in the picture.

Good luck with this