Improving the performance of the usage metrics reports is at the top of our priority. Work is in-progress which should significantly improve performance. We should have an update by end of September or October - stay tuned.
Separately - unfortunately there are no current plans to add email subscriptions to usage metrics, though I would encourage you to create/vote on the idea at ideas.powerbi.com
I've noticed that using the ViewsCount measure seems to cause most of my slow downs. I am connecting to a report usage metrics dataset on one of my workspaces through Excel and finding that almost any time I pull ViewsCount into the pivot the refresh never completes. I've waited more than 10 minutes at this point and its still trying to bring in the results.
We have a PowerShell script that executes on a scheduler job daily to extract the Power BI audit log records and writes them to a file on a shared folder where they are picked up for processing. Note, sometimes it takes more than 24 hours before the audit data is available so we had to code around this to allow for a flexible lag.
We then wrote a custom Power BI report that joins the account information pulled from these audit logs to internal data sources so we can show data at multiple levels to track usage and adoption - by department, by title, etc.