2/ Among other things, money solves a coordination problem. Trading a single good against others solves the combinatorial explosion of a barter economy. It is a scalability solution that allows coordination across large groups of people.
5/ A decentralized system can't rely on our human concept of time. A trustless, non-local time is required. Trustless, because we must not introduce a third party. Non-local because we don't have the luxury of a central frame of reference.