Unfortunately, to get parallel lines on a FileMaker line chart requires parallel fields in the records supplying the data to the chart. This can be done, but will definitely require some design work so that you get two calculation fields, one returning data from the current fiscal year and one that returns data from the previous fiscal year...
Yes, this is what i'm needing to do. Would it be possible to atleast get the found set to only show the current fiscal year instead of year single year a particular customer has ordered?
Yes, you can certainly do a date range find (where you enter date1...date2 as find criteria) to find only records for a given fiscal year.
You can also create a Fiscal year calculation field that returns a consistent year for all dates in a specified date range and perform a find for that. (Or use it in relationship.)