What is the size of the image sensor in the largest optical telescopes? What image sensors (imaging electronics) are used in telescopes? Like CCD, is that the best option?
What is the typical physical size and resolution of the photo-sensitive surface of the currently active largest ones?
The current largest digital CCD camera is that of the Vera C. Rubin Observatory1 which has a whopping 3.2 gigapixels. The previous largest features on the Panoramic Survey Telescope &amp; Rapid Response System (Pan-STARRS), and has a resolution of ~1.4 gigapixels.[1]
Based on the spec sheet provided by the Vera Rubin Observatory, the LSST camera has a resolution of roughly 0.2 arcseconds per 10 $\mu$m pixel. It is about 5 feet (1.52 meters) wide and weighs over 6000 lbs (2721 kilos, $2.6\times10^9$ dyn).[2] The actual photosensitive portion of the camera is ~64 cm ($4\times10^{34}$ Planck lengths) across.
Cameras of this size often have pointing, calibration and recording issues. These sources of error are usually extremely well understood, but it's still interesting to see. Pan-STARRS has a detailed list on their data site[3]. These issues include:

Randomly missing data that gets filled in later
Pointing errors related to astrometric positions of their targets
Registration issues near the celestial pole resulting in poor photometry

1formerly known as the Large Synoptic Sky Survey or LSST. The acronym has now been repurposed: What is the LSST now? Where does LSST end and Vera C. Rubin Observatory begin?