Is the Seesii impact wrench powerful enough for lug nuts?

It is aimed at passenger-car lug nuts and similar fasteners, and a 1/2-inch drive with multiple gears covers most of that work. Check the published torque figure against your vehicle's lug nut spec before relying on it for heavy trucks.

Does it use a standard 1/2-inch socket?

Yes. The square anvil takes standard 1/2-inch impact sockets, so common lug nut and bolt sockets fit without an adapter.

How long does the 4.0 Ah battery last?

Expect enough runtime for a set of wheels or a batch of bolts, with the exact count depending on torque setting and fastener size. A spare battery is worth having for all-day jobs.

Yes. The brushless motor is the main selling point: it runs cooler and should outlast a brushed motor, with less maintenance.

Can I use it as a drill or driver?

No. It is an impact wrench with a 1/2-inch square drive, not a chuck-based drill. For drilling or driving screws you need a separate drill or impact driver.