What to do with what I've learned when writing my research proposal?
Having learnt something new does not mean that you can publish a research article. You need some new research to publish. So my answer to the question in the title is:

Use your new knowledge to do research.

If you still hold on to the idea of publishing something, you need to think hard about 1. a venue to publish and 2. what is it that makes your text publishable. If you can write a really good overview for some audience and can find a venue that may fit, you may try (but in fact, it is pretty hard and next to impossible to write a good overview when you just entered a field, this is something for more senior people).