Short answers, pulled from the story.
The first decipherable sentence written in Egyptian dates to the 28th century BC within the Second Dynasty. This inscription was found on a seal impression inside the tomb of Seth-Peribsen at Umm el-Qa'ab.
Around 800 distinct hieroglyphs were known to exist during the Old Kingdom, Middle Kingdom, and New Kingdom eras combined. The number rose again to around 5,000 by the Ptolemaic period after decreasing to between 750 and 850 during the Middle Kingdom.
The last known inscription comes from Philae and bears the name Graffito of Esmet-Akhom dated to the 24th of August 394 AD. Monumental use ceased after the closing of all non-Christian temples in 391 AD by Emperor Theodosius I.
Jean-François Champollion achieved complete decipherment by the 1820s using the Rosetta Stone as a key. In his letter dated the 27th of September 1822 he described the system as writing figurative, symbolic, and phonetic all at once.
Egyptian hieroglyphs were added to the Unicode Standard in October 2009 with the release of version 5.2. This update introduced the Egyptian Hieroglyphs block covering code points from U+13000 to U+1342F.