Welcome. It sounds like you've come to the right place to continue building on your existing accomplishments and portfolio. I think it's fine to repost your own original content. Others may disagree, but as long as it's your content, it should be fine.
As for your other question, yes, all topics are open for exploration, especially if your purpose is to explore them and not be concerned about the rewards that you get. Not all topic are as popular as others, but if they interest you, they will probably interest others as well.