The mist will obviously not be wanted on some of those materials…acetal, acrylic, wood… The proper cutters will be far more important, and coolant can cause a lot of damage to those plastics (depends on what’s you’re using…)
With brass, chip clearance is most important in my experience, and any lubrication easily provided with a dropper. An air blast works nicely for the purpose, others use really good vacuum setups.
Aluminum is a different animal…yes, mist if you can, but a few drops here and there with a dripper (by hand) actually works quite well. I (of all people!) enjoy the over-kill of a problem, but you might want to just try it out without the additional setup first. Even a simple spray bottle is a pretty adequate “mister” for a lot of work…and a lot cheaper until you’re into what you find as being the bits you really enjoy vs things that you don’t. Endmills for aluminum are kind of specialized as well. Don’t forget that if you’re using any kind of coolant, you’ll want to keep it off your mdf wasteboard if that’s what yours is made of.
I too use isopropyl alcohol, via Home Depot, nothing special. I do not further mix it with water, and no, at the quantities being used, flammability shouldn’t be an issue.