Multi-year planning is available for use today. You should be able to create a new plan (from 1-6 years) using the Create Plan option.
I'm not certain what is contained in the 2016/2017 plan data so I'm guessing a little bit here. In order to address your specific use case you may need to manually manipulate the data in Excel for the Closing 2016 and Budget 2017 in order to combine them as year 1 and 2 of the plan. You will see the column headings for the multi-year plan reflect the proper fiscal period for each year.
The forecast can be created for April based off of the plan you created above. For example, you would load actuals for Jan-Mar 2017 and create an April forecast, selecting April as the starting month of forecast. You will then have a multi-year plan which you can then compare to a multi-year forecast.
Does that make sense? If you need to bounce ideas off of me then please let me know.