Tool question

I fitted my power brake booster last night so I had to enlarge the hole in the mount. I used a combination of a sawzall, drill, 3" air cutter, and a file to clean up the mess. I'm sure there's a "right" way to do this. So, what tool am I missing?

Similarly, what's a good tool for making cuts (particularly inside ones like for a heater) in the aluminum panels? Nibbler? Rotary cutter?

Thanks.