I'm really not sure how far out you can do the appointments. Seems like I was within 180 days when I made mine. I'd call and let them tell you if it's too soon or not.
As for locations that might be fun, I dunno. Are you wanting to the the longer, in-park session or the shorter, resort one? In-park I would say MK or maybe DHS. I would see how early they could do it. That way you don't get other people in the background so much. Epcot is pretty romantic and, I think, could be fun, too. Like y'all posing with the viking statue at Norway or something. It's what you bring to it, ya know? Bring some Mickey ears! Bring things that might make good props. I wish I had brought our ears and a balloon.