This might not be a direct answer to your questions, but it might be supplementary.

I personally subscribe to the tabula rasa mode of thinking. Not in the sense that the brain is a true blank slate at birth--genetics play a role as well. After all, consider temperament and risk factors for depression and other illnesses. And we're imbued with basic instincts like hunger and a drive to survive. But otherwise, we're a blank slate. We don't innately know language or so on.

I believe that this slate fills up over time according to what we experience in the world. We learn things according to conditioning and association--some things we learn to associate with pain, others with pleasure, and so forth. Those associations direct our behavior and make up subjectivity--tentatively, I might even wager that subjectivity is, at its core, a complex set of associations. We also learn more abstract associations like objects and concepts with sounds and visual marks--in other words, language. And because we all grow up in different contexts, the types of associations we form will have different nuances for each of us. This is why so many disagreements over language happen. For example, one person may grow up in an environment where a word is accompanied by bullying, and thus will associate that word with pain. Another person may grow up in an environment where they are never bullied using that word, and thus, the word carries neutral associations. When these two people meet, their meanings for the word will mismatch, causing confusion and possibly strife.

I personally think that forms the root of many arguments--people coming from different backgrounds and thus learning different things. Only, since humans are, well, self-centric, we unconsciously expect everyone else to have the same experiences as us, and when someone acts in a way that's a mismatch to those expectations, we explain it away as them being "stupid" or "overly sensitive" or "rude". Which, to say the least, leads to no end of unproductive argument.

You can extend it to things beyond language as well. Triggers in PTSD, for example, are associations in which usually neutral things are associated with strongly negative feelings because the formerly neutral thing was strongly present during a traumatic event. Likes associate certain things with positive feelings. Feelings themselves operate on associations--something you've been trained to perceive as positive will elicit positive emotions, negative things elicit negative emotions. Learning itself is a long process of creating associations between concepts, between terms and definitions, and so forth.

So I'd say that in order to think, something needs to be able to create associations at the very least. Of course, even a rat can make associations. So, it becomes a question of what level of association is needed to qualify as human-level thought, as well as how an entity can apply those associations. I hope I make sense.

To be honest, talking about associations like this feels like saying "math is made of numbers". It's a "well duh" thing once you think about it. But hopefully it helps somehow anyway. It was rewarding to write this.

Writing all this reminds me, too. Someone once asked me which school of psychology I subscribe most to. I honestly would be reluctant to limit myself to any particular one, especially given that I don't have a formal degree in the field, and also given that I think a lot of those schools actually explain different aspects of the same thing rather than one being "right" and the others being "wrong". But if I had to choose? Probably behaviorism.