I think you'd probably want to do these in the reverse order (i.e. Professional 1st followed by Engineer 2nd).
Best advice for doing this as cheap as possible ...
* Participate in the Developer Community joining the ambassador program which can get you an individual tenant for practicing and learning the UI.
* Work through the Mock Project (https://community.sailpoint.com/t5/Working-With-Services-Knowledge/IdentityNow-Mock-Project-and-Ment...)