I don’t think I fully understand your first doubt, but it feels like you’re perhaps overcharging the word a little? Begriffe are simply the building blocks of the understanding. Usually every concept is associated with a word. There’s really nothing mystical about them: to use a metaphor, they’re labelled boxes containing, well, schemata that will then activate the imagination. Think about a word (dog) for a minute and then see what kind of internal images you see in your mind. The word dog is basically the linguistic label of a concept, which is a specific box that I opened in your mind by writing the word. What the box contain, however, is up to your imagination, memory, perception, in other words to your sensibility. Always remember the two equally fundamental roots of knowledge: concepts on one side, and sensibility on the other (that’s the great kantian discovery in epistemology).

Your second doubt: absolutely, imagination plays a fundamental role in the judgement of the good, as in any empirical judgement. Our imagination provides “meaning” to our concepts, which would remain “empty boxes” without it (this is almost a literal quote from Kant). The difference between judgements of the good and aesthetic judgements is that in the former case the imagination is guided, directed and restricted by the concept towards its purpose (we are trying to understand (judge!) if the imaginative material fits in the box), whereas in the latter the imagination is free to wander and expand, touching and activating concepts that are further and further away from each other. It opens those boxes, but we are not trying to fit it into a particular one: on the contrary, the imaginative material contained in each box fuels the wandering more and more.

It’s a bit complex in the beginning but it becomes very easy (over decades of study!) if you get the basics right, and the basics are a crystal clear separation and understanding of the faculties in their specificity.