about renaming the column from Overall Sum of Count to something custom it looks like it's a regression issue that it doesn't exist on kibana version 6 and there are a few bug opened on github like this one https://github.com/elastic/kibana/issues/69014. I mention a quick workaround on the following topic: Custom Label field not available for MaxBucket aggregation.
I am still looking for any suggestions on how to rename the date ranges.