Are you re-taking G-Chem II with the intent of raising your science GPA (or did you take it a long time ago)? I think you should cut your loses and move on and ace organic chemistry. Re-taking may be a waste of time (unless you need to knowledge for the MCAT or are applying to osteopathic schools).
Here is my situation: I took G-Chem II (after AP chem, which placed me out of G-Chem I), in 2002 and received a C. I plan to re-take through UNE online because I do not have enough of a grasp of the material to tackle it comfortably on the MCAT. Also, I cannot find a school that offers it in the evening over summer in the Bay Area (I have taken all my other chem classes).
I think in your case that repeating a class that you already took in a standard classroom, online is a tad bit of a waste. The classes are viewed to be inferior so getting an A in it will not prove anything. But, if you have no choice, and need the knowledge as a refresher or for the MCAT, then go for it.
As for your second question, you can other courses during the glide year. Biochem and physiology are helpful for the MCAT from the practice test I've attempted, but definitely not required.