Hey, the blueprint system will be fine for this, don’t worry about having to learn C++.
This is a good intro video to make sure you can set up on a phone, and goes through the uses of the template. Just skip to the AR section.
Next you’ll want to take a look at this documentation. Specifically the “Scanning and Object Placement” part
After that, you need to look into “Line Trace By channel” using a “Touch Input” to basically draw a line forward where you touch the device, then grab what is touched and have it do something. In this case you want to spawn a Widget, so you want to go learn about those once you can get the actor to appear in the world! Don’t be afraid to come back here and ask questions!
Edit: Since you’re experienced with Unity, a lot of these concepts are going to make sense, they’re simply renamed and visualized instead of being straight text. Don’t stress, just be diligent and I have confidence you’ll be fine!