Thought it might be good to have ability to start a review on provider, and save the template until refined for final submission - giving the ability to make changes, correct errors etc.

Another excellent idea, I hope you moderator's are passing these on to the powers that be!

It ain't much, but if you go to the Account Aanager immediately after submitting a review, you will notice that there is an "edit" button next to it.  You do have the ability to edit a review for a very brief time after submission, no more than a few hours at best.

A far cry from the several days minimum that might be required.  I usually wait a few days before submitting a review, unless the experience was horrendous.