Is the Milwaukee M18 Fuel drill worth it over the brushed M18 drill?

Yes for frequent or heavy use. The Fuel version adds a brushless motor, more torque and better electronics, which pays off on big bits and daily job-site work. For occasional light tasks the brushed model is enough.

Does it come with a battery and charger?

Most versions are bare tool only, so you need an M18 battery and charger. Kit versions bundle them, so check which one you are buying.

How does it compare with the DeWalt 20V Max XR drill?

The Milwaukee generally has more torque and a sturdier chuck, while the DeWalt is lighter and often cheaper as a kit. Both are brushless trade-grade drills; pick the battery platform you already own.

What size chuck does it have?

It has a 1/2-inch all-metal keyless chuck, which takes standard round and hex shank bits up to 1/2 inch.

Can it drive screws as well as drill?

Yes. It has forward and reverse and a clutch with adjustable torque settings, so it works as a drill/driver, though a compact impact driver is faster for long screw runs.