What can a 50W panel actually power?

It is a maintainer, not a generator. Expect roughly 2 to 3 amps in good sun at 18V, enough to keep a deep-cycle battery charged or run small 12V loads like lights and a phone charger through a battery.

Is the MPPT controller worth it over PWM?

Yes for this size. MPPT converts excess panel voltage into extra charging current, so it holds up better in heat and partial shade than the PWM controllers usually bundled with 50W kits.

Can I connect it straight to a battery?

Yes. The 3m clamp cable goes from the controller's battery output to the terminals. Connect the battery first, then the panel, so the controller reads system voltage correctly.

Does it come with mounting hardware?

No. The kit is the panel, the MPPT controller, the clamp cable and connector leads. You supply brackets, a stand or a tie-down for the panel.

Is it weatherproof enough to leave outside?

The panel is built for outdoor use with tempered glass and an aluminum frame, and the controller is waterproof. Still mount the controller where it is shaded and not sitting in standing water.

Can I add a second panel later?

Check the controller's voltage and current rating first. A second 18V panel in parallel may exceed a small controller's limit, so confirm the rating before expanding.