Hi Shawn,
Although we could combine all of these aspects into a single chart using our Magic Reports solution, if you'd (first) like to model these using built in Workfront reporting, I'd suggest you start with three separate reports, (perhaps shown next to each other in a three-column dashboard) since Workfront only supports one horizontal axis per report.
By doing so, you could show Total Per Month, Added This Month, and Completed This Month (e.g. as a bar chart for each), but noting that each will have its own filter and axis (e.g. Entry Date, Entry Date, and Actual Completion Date, respectively).
I suspect first one might not be possible, btw, if you're trying to capture how many were in a queue "at that time, over time", unless you noodle out a way of recording those stats over time.
Regards,
Doug