I haven't read beyond the first post.
My son skipped 1st grade making the move to 2nd at the beginning of the school year. If you have the option of skipping now I would take it.
We found it was difficult to have missed the writting and simply the structure of 1st grade going into second. My son got nothing out of the 2nd half of K, but probably would have gotten something out of the second 1/2 of 1st and would have been more prepared for the demands of 2nd.
Now I'll go back and read all the responses and probably have additional to say.