Frankly, if someone wanted to fully answer all four questions you asked (especially the first two) it would turn into a whole essay. The most important thing is not to try to write something amazing outright; personally, I say it's to slowly but surely improve the little things you notice can be done better.
To start with though, when you're creating the world, the characters, the power system, or basically whatever, I can tell from experience, don't try to make them perfect. It sucks up a massive amount of time and doesn't benefit your story much. It's generally way better to make something you like, focusing only on 2-4 key points, and flesh out the details as you write more, or don't specify them at all. Reader's imagination is way more powerful than some people think and will fill out those details by itself.
In regards to those 2-4 key points, this is actually an rule I made for myself after I caught myself overdescribing things because I wanted details. It says, when describing something, focus only on a few most important or noticeable points, add a general impression (either in narration, or in dialogue), and move on. Anything more than that will probably be too much descriptions and bore your readers; you can keep to it or not, but I personally found it really helpful.
Then, backwards to power systems and worldbuilding specifically, my advice is to clearly define each major element, why it's there, how it's gonna affect a story. Not in some great detail and not necessarily to readers, but just so you know it's there for a reason, not as a gimmick that wouldn't change anything if it disappeared. I've seen way too many stories that introduced a cool mechanic only to abandon it halfway in because the author decided it's not necessary, or others that described a whole world only not to touch three fourths of it, and I made both damn mistakes.
And generally, keep things simple, don't try to add weird twists without good reasons to. Creativity is good and I'll say it now that I'm not trying to limit yours in any way, but for a story to work, it's got to be kept in some bounds or you'll get pizza with scambled eggs and fruit salad.
