Waterfall Chart Best Practices

Hi - could someone please share some best practices for setting up waterfall charts?

I’m trying to create a bridge: Starting Headcount, New Hires, Terminations, Ending Headcount

Question 1: does the formula in Ending Headcount have to be “Starting Headcount + New Hires + Terminations”? It seems like yes if I want to create a Contribution Waterfall Chart. In this scenario I’d have to create an Iterative Calculation and use the “PreviousOf” function for the starting headcount, right? Or is there a better way?

Question 2: Is there a way to make the periods that are shown in the chart dynamic based on the page selectors? We’d like our users to be able to select which months to see. For example, if they select June and September, they should see a waterfall with June Starting Headcount, all New Hires and Terminations for June/July/August/September, and then Ending Headcount for September. Is this possible?

Question 3: is there a reason I can’t control the Aggregator Settings in the chart? This has been causing issues with Question #2 above

Would appreciate anyone willing to share best practices here, as I haven’t found the documentation to be particularly helpful on this subject. Thanks in advance!