First you need to take into account the limitations of your machine. As I said above, a vertical turret mill is not a production machine and you can't expect it to do the work of a production machine. You have a 3V frame machine, and mine is a 4V frame, about 1000 lbs heavier than yours. Same HP and head. I normally use 1/4'' to 1/2'' cutters on mine depending on the job. 1/2'' cutters are about all the machine will take and still remain stable. There are times I have used larger cutters when a lot of stick out is required, but the feed speed and depth of cut needs to be adjusted for the larger diameter cutters.

For all practical purposes the 2024 and 6061 can be treated the same. I prefer aluminum cutting 2 or 3 flute carbide endmills, about 40% step over, up to 2X dia for depth of cut, and a chip load of 0.001'' to 0.002''. Adjust the feed speed to what the machine will take and the RPM to meet the chip load requirement. There is no way you can exceed the SFM limitation of the endmill. Spray mist coolant. I have never worked with 2024, but I understand that it is less gummy than 6061 and thus a bit nicer to work with.

For mild steel, you can pretty much treat it like aluminum. I normally use 4 flute carbide endmills designed for steel cutting. Again adjusting the feed and speed to maintain a 0.001'' to 0.002'' chip load. Maybe 30% step over and a bit less depth of cut. Spray mist coolant.

In either case, you can feel when the machine is happy. I normally use feed speeds in the range of 5 to 30 IPM. If it starts vibrating you are pushing it too hard, if you are getting a lot of chatter, then try a bit more feed speed or a bit lower RPM. You will notice I did not address SFM, you will always be below the limitations of the end mill, the chip load is the important parameter. You need a heavy enough chip load to make sure the tool is cutting and not rubbing, but you also need to stay within the limitations of the machine.

If we were having this discussion about a production machine, then all of the suggestions above would be different.