How many injection points are necessary for a fat transfer to your breasts?

Every surgeon's technique is different. What's done is done and you are left with permanent scars. You are right, one of the advantages of fat graft breast augmentation is to do it without scars and also contour the body from where the fat was collected. I personally use two needle poke holes through the skin, one lateral to the breast and one in the breast crease. With a special curved blunt cannula, I can reach all quadrants of the breasts without difficulty. Occasionally I place a needle poke hole in the areola. These heal without a noticeable scar. The liposuction poke holes are placed in "stealth" locations, again with no stigmata that you had liposuction. BTW, the needle poke holes do not need to be sutured. Sorry to hear about your experience.

There are many acceptable techniques that varies with the surgeons experience which include what you described. In my practice I typically use a needle puncture wound for the fat injection cannula so no stitches or scars are typically seen.

Im sorry about your scars.  If you are fair, various laser resurfacing may help fade them somewhat.  Every surgeon has their own technique.  In our practice the fat transfer injection sites are 2-3 per breast and needle size hole which would leave a very small scar and usually doesn't need a stitch.  Two of them are placed in the crease so they are less visible and one on the outside aspect of the breast.  

are surgeon dependent and need for sutures dependent on what size cannulas are used in fat transfers.  I'm sorry your procedure left you with undesired scars  In my practice, you will get at least 4 access wounds for each breast and possibly smaller ones (that don't require sutures) for finer grafting.  The bottom line is how successful was your grafting?  If you achieved your size goals and look, then its hard to criticize the number of access sites used.

Its hard to comment on your special case without seeing the operative report and pictures.In general, fat grafting does not require incisions but small needle holes to place the fat.  You are correct in stating that this is one of its advantages.  The sites don't require sutures.