skin elasticity depends on a number of factors--age, number of times we've lost and gained, genetic 'luck', rate of loss, etc. Wait two years after hitting goal weight until you judge how your skin is doing--there's some "catch up" time where it will continue to shrink. If then, it bothers you, cosmetic surgery is an option. I believe that most people, upon getting slim, will have improved their self-confidence so much that some small issue like stretch marks or a bit of excess skin won't bother them. If someone judges you harshly for such a thing, they're not worth your trouble.

On LC and muscle loss--the opposite of what you fear is true. On low-cal diets, what you lose is some fat and some muscle, which is one part of why metabolic slow down results from such dieting. On LC, you lose almost no muscle tissue. (see http://www.lowcarbretreat.com/josh_yelon/topic2.html and DANDR)

With weight lifting and keeping my protein grams at 100 or more, I estimate I've increased my lean body mass 12-13 pounds in a year, in addition to losing the 25 pounds of scale weight...in other words, I've lost 37-8 pounds of pure fat while adding muscle. Not a bad deal at all!