Create reservations on Compute Engine and BigQuery. You can reserve capacity in advance and use it over a period of time. You could also get a cost advantage.
=> There is no need for involved support. It is self-serve via the console.
=> You can reserve resources in advance when you have the need for it. And when you want to take a pay-per-use approach, that is also possible.
=> It is not a good idea to be lock in/hoard resources; you'll pay unnecessarily for resources. Also, it is difficult to time exactly when the demand will be.
References:
https://cloud.google.com/compute/docs/instances/reserving-zonal-resources
https://cloud.google.com/bigquery/docs/reservations-intro