Maxillary Impaction Followed by Gum Contouring/bonding?

Yes, you should be able to have gum recontouring & cosmetic bonding without compromising your jaw surgery, but FIRST, you'll need permission from both your oral surgeon & your orthodontist, or whoever has treated you.  Only they will know when you have healed adequately and are in a stable enough condition.   Gum tissue contouring can be done very predictably with a diode soft tissue laser.   Most of the time, it is best to wait for the braces to be off so that the teeth and gums have settled into position.  If you rush this, your results may not be as stable and it may need to be retreated with another laser procedure.  Also the cosmetic bonding needs to wait until the braces are off.  Sounds like your results will be amazing!  

The answer is yes to all of your questions.  After one month of uneventful healign you should be able to have your gums contoured without any issue.  Make sure to have your oral and maxillofacial surgeron ok this and even perform the procedure for you.

To play it safe I would wait six weeks following the LeFort orthognathic surgery you had.  Six weeks will allow the bone to stabilize without any disturbance from another procedure.  Gum re-contouring can be done with your braces on but I would defer it till the braces are off.  Once the braces are off the final position of your teeth will be present so proper symmetry could be followed.  An exception might be doing some gum re-contouring if your gums are very puffy / inflamed due to the braces.  These type of gum re-contouring can be achieved with hard tissue laser (Erbium laser) or soft tissue laser (Diode laser).  The small chipped bonded restoration can be done any time since it  should not interfere with the bone or gums.