How does craving (taṇhā) relate to neutral feelings?
Taṇhā doesn't automatically have to relate to neutral feelings. Remember, the twelve links of dependent origination are talking about nessisary causation, not sufficient causation, so when the Buddha says


  [W]ith feeling as condition, craving [comes to be]


the meaning is that feeling is necessary for craving to arise, and without feeling, craving can never arise. But it does not mean that if there is feeling, craving will always arise.