At what speed, or how long will the initial data transfer take?

Our two-way transfer rate averages from 1GB to about 10GB per hour per account (240GB per day per account).
Our one-way migration transfer rate is up to 1TB per day per account.
Systems like Google Drive and have more strict requirements. For example, Google Drive permits, approximately 500GB to 750GB daily for Shared Drives. You read upload limits on the following page:
Google Drive Usage limits
More discussiont on this topic can be found in the support note

How to maintain cloudHQ_archive?

If you are using Amazon S3 backup we recommend configuring an S3 policy to transition files older than 90 days (approximately 3 months) to Glacier or Deep Archive storage as explained in the articlealias (how to purge)