I will try to split down all your questions...
If that is true, perhaps having spring-boot application to run the Activiti engine and Rest service and then running the wrapper application can serve a BPM UI made with the ADF angular 4 components. To be able to use the ADF Angular components library, you need to use APS, Acitiviti is not supported.
Please clarify what minimum components need to be installed to get angular 4 going. Do I need to download entire Alfresco community edition application?
You can find this information on the prerequisite page of the Alfresco Angular Components repository, more information is also available on our community portal