For those of us who view the biblical account of creation as figurative, rather than literal, we can see incredible and rich symbolism. First, the seven day thing. We know there is no natural phenomenon that has a cycle of seven days (day, month, year all do). So obviously the division of time was a creation of man. We know too, the seven day division predates the Jews’ use of it. But it really doesn’t matter whom created it, in Christianity, seven represents perfection. The use of the seven day cycle then, extablishes that God created a perfect world (and universe for that matter).
As to the steps of creation. As you’ve pointed out, from a literal standpoint, it doesn’t make a lot of sense, but from a figurative standpoint, there is a very distinctive pattern. The author lays out an order to creation, from least important to most important (and obviously the sun/moon were more important than plants). It establishes then that humans were the most important thing that God created.
There’s probably other symbolism present, but these are the two I think most important.