Only a tiny bit of help here - ds is 11 weeks and I'm still not sure of the answers to all the questions.
On whether your breasts are empty, I've thought quite a few times that mine must be, as ds pulled away or started to grizzle. But every time whe I tried to hand express - I'm not very good at it, but can do it for a few seconds - there was always something left. Maybe it was harder to get to, though?
On single side feeding, I have been trying from the start and have probably had about ten feeds all told where ds hasn't also wanted at least a few minutes from the other breast.
On using the breast as a dummy, I've tried to just be relaxed about it and regard it as bonding time (hope that doesn't sound too precious) but it did mean that it was about 9 weeks before I stopped getting sore nipples, as ds was on the breast for 6 to 8 hours a day.
Think that around 6 weeks is growth spurt time for a lot of babies.
On the being hungry question, I wish I knew! I do know from trial and error that when I "overfeed" ds - e.g. when he's grizzly and won't seem to settle he seems to bring it back up (not spectacularly but gently) and so I know that he won't take more than he needs. So I work on the basis that he will cry if he is hungry and if I overfeed him a bit because I feed him in response to a cry that wasn't hunger, it isn't the end of the world.
Sorry - bit long. hth.