Q1: You can either use Azure Monitor (https://learn.microsoft.com/en-us/azure/data-explorer/using-diagnostic-logs?tabs=ingestion#set-up-diagnostic-logs-for-an-azure-data-explorer-cluster) and the you can analyze the activity (https://learn.microsoft.com/en-us/azure/data-explorer/using-metrics)
You can also use the .show queries command (https://learn.microsoft.com/en-us/azure/data-explorer/kusto/management/queries) - .show queries | count
Q2: Try to summarize by startofweek(date)