Then the definitions are done and the hard thinking is paid for. What is left is removing the human from the assembly, which is the part Excel cannot do.
Whatever holds the truth. The roll-up is platform-agnostic by design; each source contributes what it knows and keeps its job.
As current as the sources allow: typically same-day, on a schedule you pick. The honest constraint is the source systems' own rhythm, and the roll-up shows its own timestamp so nobody guesses.