Transpose Too Complex? File too big? What to do?

I am working on transitioning POS data from Excel to PowerBi because the file is growing too big to update (600MB).  Right now, each row is one item with both repeated columns of identifier data and unique columns of weekly sales data.  It amounts to about 600 columns for each row, so there is a lot of stuff.  

I have two issues. 

1.  I want to be able to show sales data on a weekly chart, but because of the format of the data, it only comes out in a vertical line on a line chart.  How do I get the chart to work?

2.  The file is going to be too big to update soon.  Currently, another analyst takes the POS data from the respective accounts and combines/cleans it into the big file.  I think there is a way to replace this process with PowerBi and my plan is to just have the weekly data live on sharepoint and be updated weekly when it gets pulled.  Then I'll use the steps in Query to autoclean/format the data into a more usable tool similar to his report but living in the cloud.  Does this make sense?

Sorry for the naivety, I'm very new to PowerBi and have only taken a new users course.