Is a chin & jaw implant/augmentation with rhinoplasty risky? Can I have them both done together under only local anestesia with sedation?

Mild risk. Every surgery carries some risk. However, smaller, quicker procedures are generally less risky than complicated, longer procedures. A chin augmentation can be combined with a rhinoplasty and done safely under local anesthesia with sedation. I would suggest making sure your surgeon and/or anesthetist is acls certified, and that your surgeon is certified by the american board of plastic surgery.
Rhinoplasty/chin. It is very common to have rhinoplasty and chin implant performed on the same day. The procedures compliment each other in terms of establishing facial harmony. The type of anesthesia is something you must discuss with your surgeon. Be sure to have your nose evaluated by a board certified facial plastic and reconstructive surgeon with expertise in nasal surgery.