Im the new guy here but with 35+ years as a cop. You can wait for an attorney as long as you want BUT the report wont wait and chances are your title in the report (Victim or Suspect) very much will matter whether you talk or wait. Once listed as a SUSPECT nothing will change that. You can wait if you want but the investigation wont wait AND any evidence you fail to point out may not be found or even be part of the investigation.
Im not suggesting you blabber away uncontrollably. When youre involved in an incident (especially a shooting), start with 911. Tell them who you are, where you are, and a brief statement of what happened. When the officers arrive, tell they why you "had" to do what you did. Dont just tell them, you were afraid; explain why you were afraid, and maybe why you couldnt retreat. You have to make the officer(s) and detectives understand what happened from your perspective BEFORE they write the report, BEFORE they leave the scene. Tell them if you have a medical condition (heart condition, breathing issues, etc). Dont be afraid to ask for EMS, chances are your blood pressure will be HIGH and your heart rate racing. Whatever you tell the medics will be part of the case and can help your explanation of the incident. A young officer may not immediately understand why you couldnt run away but tell him you left half a lung in Iraq or you have... and it might just make him understand why you acted the way you did.
Short statements like "I was afraid" or "he had a gun" wont work. Telling them you will cooperate once your lawyer gets there is a mistake. First most cops dont really like defense attorneys because of the way theyve been treated in court. Second anything you fail to point out may not be there when they get around to going back to look. If the bad guy had a partner and he took the gun and left, hes long gone when your attorney says its OK to talk. If the gun got tossed in the woods, down the sewer, on on the roof no one is looking UNLESS you tell them
Wait for a lawyer and you can bet he'll be sleeping at home that night; but your chances are 50/50.