As far as how long you should wait to do anything physical, I'd say don't do anything unless you actually like her and want this to get more serious, (or can at least see it getting more serious.) Basically, don't lead her on just because you think you're "supposed" to kiss her, if you're really not sure you want to stay with her. It doesn't sound like you're that sure about it. Spend more time with her - eventually you will get past the barrier of "friendly talk" if the two of you have a lot in common and a lot of chemistry. If you seem to stay at that barrier without getting any closer and more comfortable with each other, I'd take that as a sign that maybe you're not "meant" each other - and it would be much easier to break it off if you haven't led her on by kissing her or more.