Yes — this extension is also available for free on kunemann.com. This Superhive listing exists purely as a way to support development; buying it here is optional, and gratefully accepted.

Yes. Patchwork is built entirely from standard shader nodes, so the anti-tiling blend renders the same in Cycles and Eevee — nothing engine-specific is required.

No — it is non-destructive. Apply moves your Image Texture nodes into a Patchwork group and rebuilds the connections; Remove from Material puts the originals back in the main tree exactly as they were.