Short answers, pulled from the story.
The oldest recognized epic is the Epic of Gilgamesh, recorded in ancient Sumer during the Neo-Sumerian Empire and dated to approximately 2500-1300 BCE. It details the exploits of Gilgamesh, the king of Uruk, who is regarded as a largely legendary or mythical figure despite being recognized as a historical person.
The ancient Indian Mahabharata, composed roughly between the 3rd century BC and the 3rd century AD, is the longest written epic from antiquity. It consists of around 100,000 shlokas, or more than 200,000 verse lines, totaling approximately 1.8 million words, making it about ten times the combined length of Homer's Iliad and Odyssey.
Harmon and Holman (1999) list ten characteristics: the narrative begins in medias res; the setting spans many nations or the universe; the poem opens with an invocation to a muse; it begins with a statement of theme; it uses epithets and epic catalogues; it features long formal speeches; divine forces intervene in human affairs; the hero embodies civilizational values; and the hero often descends into an underworld.
Ancient Greek epics were composed in dactylic hexameter. Early Latin poets used Saturnian meter, but by the time of Ennius, Latin poets had also adopted dactylic hexameter. Henry Wadsworth Longfellow adapted dactylic hexameter for English in his poem "Evangeline."
Milman Parry and Albert Lord were early twentieth-century scholars who studied living oral epic traditions in the Balkans. They demonstrated that oral epics are built from short episodes of equal status to facilitate memorization, and argued that the written texts of Homer's epics most likely originated as dictations from oral performances.
An epyllion, meaning "little epic," is a brief narrative poem with a romantic or mythological theme. The term came into use in the nineteenth century and refers primarily to shorter hexameter poems of the Hellenistic period. The most famous classical example is Catullus 64. It is distinct from mock epic, which treats humble subjects in elevated style for comic purposes.