I'm pretty new at all this, but a few things struck me about your post. First- it's commendable that you want to help your sister move out- but did she actually say to you that she wanted out? Have you two talked about this before you move and decided how to do it? I'm concerned that if she didn't actually ask you to help her, you might be disappointed in the results. She is not actually a kid any longer. However, even if she doesn't come to live with you, having you around may be a very positive change.
As for the last two questions, they are related. You can't actually help codependents until they are ready to BE helped of their own accord. You also can't maintain your own sanity while trying to help people who don't necessarily think they need help. What you can do is.... take care of yourself first. Really. I am not religious, yet I've found that Al-Anon is still very helpful for me. They tell you to interpret "higher power" however you see fit, take what works and leave the rest. Don't let the God thing get in your way.