Pareto Chart and table by Period

I have 5yrs of historical data where I need to provide a chart that tells me how many 'Customers' contributed to the Top 80% of sales

I have managed to get this far by using RANKX (Refer image)
1RANK = RANKX(ALL(lookupPartner[Partner Id w Name]),[Actuals Historical],,DESC)
Actuals Historical Cumulative = CALCULATE([Actuals Historical],TOPN([1RANK],ALLSELECTED(lookupPartner[Partner Id w Name]),[Actuals Historical]))

Actuals Historical Cumulative % = DIVIDE([Actuals Historical Cumulative], [Actuals Historical (partnerID all selected)])

Issues

1) I dont know how to write a DAX that only COUNT the number of customers giving me Top 80% of Sales (highlighted in Green in the image). I dont want to use to use the FILTER pane

2) I dont know how to write a DAX to help me provide below (including a bar chart)

FY16 FY17 FY18 FY19 FY20
No. Customers contributing to Top80% of Sales 100 85 95 110 115