Yes. You can use the aggregate goal to aggregate multiple trace reports into one aggregated report.
No. The plugin will skip your module if it does not have traceability properties defined.
Yes. The aggregator is meant to aggregate multiple tracer reports into one. You can simply use the tracer only to generator a report per maven module.
No. The aggregator can only aggregate reports generated by the tracer. Without tracer, the aggregator is pointless.