Hello,
If so, technically you can use R4. However, our tutorial App was created specifically keeping DSTU2 in mind. And also have added a note for the same
Note: This tutorial is in the process of being updated for the newer version of FHIR - R4. Outside of this tutorial, the use of R4 over DSTU2 is encouraged.
You can host your app whenever you need as long as its connected to the internet.
Thanks,
Fenil