The one issue with the Mazda3 is negative camber, because it's not adjustable without buying additional hardware.
The front will end up around -0.5 degree more negative and the rear up to -1.0 degree more negative than stock.
What I would do is try to measure the camber, both front and rear, with the factory springs. If you're between 0 and -1.0 it'll be O.K., but note the inside of the tires will wear more quickly than the outside.
If either front or rear is greater than -1.0 degrees then you should definitely either get the Mazdaspeed rear camber links, or some adjustable rear camber links like the SPC's.
You will also need to re-align both the front and rear toe after lowering. This is the most common reason people experience excessive tire wear, they don't keep the front and rear toe properly aligned.
Unfortunately, I don't believe there's a readily available front camber adjustment kit for the 3.
I'm sure you'll get some other opinions, but these should be some good guidelines.
