Is this impact driver good for deck building?

Yes. Its torque is enough for deck screws and most lag bolts, and the brushless motor handles repeated driving. For very large structural lags, a dedicated high-torque impact wrench is better.

Does it come with a battery and charger?

The 324B-03 is commonly sold as a bare tool, so check the listing for what is included. It uses Kobalt 24V batteries, which also fit other tools on that platform.

What bits does it take?

It has a 1/4-inch hex chuck, so it takes standard 1/4-inch hex driver bits and bit holders. No special bits are needed.

How does it compare with an 18V driver?

It offers comparable or slightly higher torque thanks to the 24V platform, but it is generally larger and heavier than 18V drivers from Ryobi or DeWalt. Choose it if you are already on Kobalt's 24V batteries.

Does it have speed settings?

Yes, it has a multi-mode selector for different fastening tasks, plus a variable-speed trigger. That helps when driving small screws or working in delicate materials.