I agree, FRA is a very large and confusing airport to transit. I've just started to remeber a few "landmarks", but one can get lost very easily in this sprawling airport.

The lounges are always very full. Not much of a relaxing atmosphere, in my experience. My advice is to get to your departure gate early, at least an hour before boarding. While LH flights are super-reliable on pushing back on time, it seems like there are a lot of unforeseen delays, security checkpoint, changed gates to make things interesting.