Does it need wiring or an electrician?

No. The solar cell charges a battery inside the fixture, so it mounts on the wall and runs on its own. You only need a spot with direct daylight.

How long does it stay lit at night?

That depends on the charge it gets during the day. A panel in full sun gives the longest run; a shaded wall or a cloudy stretch shortens it noticeably.

Where should I mount it?

Put it where the solar panel faces the sun for most of the day, such as a south-facing fence, gate post or shed wall. Avoid deep shade under eaves or trees.

Is it bright enough to light a walkway?

It works best as an accent or marker light along paths, fences and porches. For lighting steps or a doorway clearly, a wired fixture with higher output is the better choice.

Is it weatherproof for year-round outdoor use?

It is built for outdoor walls, but check that the mounting spot drains well and that the panel stays clear of snow and leaves so charging does not stall.