“In contrast, during unplanned times when I’m simply lying back and my mind is calm and start thinking about concepts, things start clicking and connecting and makes sense. I’d describe these as epiphanies/”aha” moments. But the unusual thing is, when I’m thinking about these concepts, I’m not in silence. Meaning, I get these realizations when I am talking to myself out loud or when writing these thoughts down. In other words I seem to not get benefit from silent thinking(sankappa), but I do notice benefits when I engage in vaca and writing-I seem to understand better via these two methods.”
This is really true.
Bhavana is NOT just formal meditation. Some people think bhavana requires one to sit like a statue. Many of those people just focus their mind on the breath, which is really a waste of time.
One could be consciously thinking or talking (both involve vaci sankhara), and even engage in writing (involving kaya sankhara) while doing bhavana.
On the other hand, mano sankhara arise automatically (when a sense input comes in), and are not really involved in bhavana.
By the way, Samma Sankappa are conscious thoughts. They are really vaci sankhara (talking to oneself), which is what you seem to be doing. Based on Samma Sankappa, one speaks out (Samma Vaca) and does bodily actions (Samma Kammanata).
So, everything you are doing seem to be correct. Listening to Dhamma discourses (and reading) are also strong aspects of bhavana.
Basically, bhavana is any activity that helps makes progress on the Path.