All I can tell you is our own experience. DS showed a similar skill level to what you describe at age 4. We had him in a private Kindergarten program at that time and his writing was very rough. Three months later, he started the public Kindergarten. They did lots of coloring and writing practice which I think was really beneficial for him and paved the way for a successful skip to first grade midyear. In his case, he had not formed any close friendships in the Kindergarten class and was eager to try first grade. So moving mid-year was not a problem.
