As for the clips that hold trim you need 5 for the top trim.
If your Dad was a welder then he might know how to shrink metal to get it straight again, a lot of body shops do it. Simple but takes hours, heat it with a torch then with a wet rag with ice cubes in it put it directly on the spot you just heated up, you do this after the seam is completely welded of course.
Also it will help if you put a lap joint in the new connecting metal to slide under the old existing roof, it will help with both the welding an to help keep it straight. There is a tool that goes on the end of a air hammer that makes the little channel, its cheap.
Once your done welding it together put a layer of Metal bondo(Aluminum grindings) stuff gets rock hard even against a grinder, so just a thin layer an then finish off with normal bondo if needed.
Just some ideas for you !