How much to cut when doing rust repair?

[67C10Step]

I am FAR from doing any major body work or panel replacement on my truck but I'm starting to think down that road.

On my floor boards the inner and outer rockers are obviously going to need to be replaced but I am torn on what to do in the floor. It is bad in the kick panel area to about six inches in and about ten inches back. I know you can purchase the floor panel that goes all the way to the hump but I am thinking I would cut out only what is necessary to get back to solid metal and keep as much of the original steel as possible.

Thoughts and experiences? How many of you have abandoned your interior fresh air vents due to rust? Mine don't look so hot, particularly around the bottom, curved area around the damper hole.