How long should a person wait before considering having a prosthesis?

Months. It is best to wait months before being fitted for a prosthesis. The reason for this is to allow the leg "stump" swelling to go down completely and to allow the stable long-term stump shape to form. Stump shrinker socks are great for this. Otherwise, the prosthesis mold will not fit properly and not work. Plus, it is not cheap to be refitted!
Depends. Assuming no issues with postoperative complications most people would wait six to eight weeks to make sure the wound is strong enough to withstand wearing the prosthesis.