Welcome and thank you for going it a try. 

Note that UNA PowerApps subscription is not absolutely required. If you stop a subscription you just stop getting automatic updates for those apps. 

As for Dolphin - we are constantly looking at ways to transition people from it to UNA effectively, but as you may guess it’s a massive challenge. From the very beginning Dolphin has been developed without much planning - it evolved according to client requests and business considerations, but when we decided to actually plan, design and engineer the framework we realised that it would have to be different - thus UNA was born. In UNA we have designed a robust data model and methods that form the base we can use for a long time - it is great for scaleing, module separation, security, etc. Base ideas is similar to, say, Drupal, with some improvements relevant for community sites.