For everyday driving I would try not to go for a too aggressive cam, unless it is offset with a change in diff ratio as well, but too high diff ratio also makes the car not so nice as a daily drive, depending on what you do, lots of city driving then its not to much of an issue, but if you do lot of highway driving it will increase the cruising RPM too much.
One thing to always keep in mind with NA modifications apart from the standard exhaust, filter and chip stuff, is it tends to exchange low and low-mid range torque for peak power and this in essence make a car not so nice to drive everyday, since you won't be driving your car in the higher RPM ranges all the time. Less torque also negatively affects fuel consumption in city driving, and the M3 is not the most economical car to start off with.
Though I would be the first one to say get a big brake upgrade, as I am a big fan of them, you will only really need it for track use, but you could get away with a lot less for a lot less for track applications. As for powerbrake I have no personal experience with them but I have heard a lot of good things about them so they are definitely worth a look.
As for coilovers, from what I have read they are a very good upgrade for the standard suspension, and because you can set things like spring rate damper stiffness they are actually sensible on an everyday road car as well, just be sure to do research as the a specific kit's height adjustability range to be sure you get one than you can set high enough for everyday use, but i don't think this should be too much of a problem.
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