Only 2 reasons to stir or mix: to aerate and to get an accurate OG. If doing a repeat of a recipe, just toss it in, no order, no mix. If the yeast don't like it, well, they can complain on this forum.
Sanitizing: If you have a sealed commercial package of sugar, corn or table, it probably does not have to be boiled. I've got 10 ales and 8 wines so far, with no boiling. I buy my sugar in bulk, put the bag in a clean poly bag, sanitize the area around the opening, wear rubber gloves, open and spoon it out. close when done. Make sure not to fold the outside of the bag inward. better yet, leave it alone and close the poly bag.