Is the Kawai ES920 actually a stage piano?

Technically, Kawai markets it as a Digital Piano rather than a Stage Piano. The distinction is real: it has fewer stage-specific controls (no drawbars, fewer assignable knobs) than the CK88 or RD-88 EX. But its action quality, Bluetooth Audio, MIDI, and built-in speakers make it a legitimate gig option — especially for solo piano players, lounge work, or acoustic-duo settings where piano feel matters more than on-the-fly sound shaping.

Which has the most realistic action for classical playing?

The Kawai ES920's Responsive Hammer III. It has triple-sensor detection, counterweights, and let-off simulation — the three features that separate "weighted key" from "piano-like action." The Roland RD-88 EX's PHA-4 is a very close second and costs about $220 less. The Yamaha CK88's GHS action is the lightest of the three and the least suited for serious classical technique.

Which one works best for busking or outdoor gigs?

The Yamaha CK88, without question. It's the only one of the three that runs on 8 AA batteries, and at 13.1 kg it's also the lightest. Combined with built-in speakers and one-to-one controls, it's the most self-contained rig of the three.

Do any of these come with a stand or pedal?

No — at this price bracket, stands and sustain pedals are almost always sold separately. Budget $75–$150 for a sturdy X-stand or Z-stand, and $30–$60 for a half-damper-capable sustain pedal (important for the RD-88 EX and ES920, both of which support continuous damper data).

Can these replace a software rig like MainStage?

Partially. The Roland RD-88 EX has dedicated DAW control modes for MainStage and Logic, so it can front a hybrid rig. The Yamaha CK88 has USB audio/MIDI in both directions, which also works well for a laptop-based live setup. The Kawai ES920 is the least suited for a software rig — it's built as a standalone piano first.