What are the major ancient literature on Judaic mysticism and spiritual development? By ancient I mean B.C.E.
I also would appreciate if you can also provide links to online English translations if it is possible.
The books you are looking for are called "Merkavah" and "Heichalot" literature. These are based on the "Merkava" (Chariot) described in Ezekiel.
I do not know if they date back to "BCE", because the way that we date modern writings it's impossible to know, but they are darn close to 0 anyways. They certainly date to the time of the Talmud if not earlier. As far as I am aware, there are no Jewish texts currently used which are dated before 0 outside of the Tanach by modern scholars (which is what made the dead sea scrolls such a huge find since it pushed some texts further back than earlierly recognized)
The earliest mystical writings in Judaism of course though belong to specific passages of Tanach. (the saphire brick work mentioned in the passages of the 10 commandments, the Seraphim and angles of Bereshit and the Prophets etc.)
Some quick links I found from wikipeida..
Apparently, the Sefer Yetzirah also qualifies as Ancient.
The Dead Sea Scrolls prove that the Jewish mystical tradition of divine union went back to the first, perhaps even the third century B.C.E. Jewish mysticism has its origins in Greek mysticism, a system of belief which included reincarnation. Among the Dead Sea Scrolls, some of the hymns found are similar to the Hekhaloth hymns of the Jewish mystics. One text of hymns gives us clear evidence of Jewish mysticism. The text is called "Songs of the Sabbath Sacrifice." Fragments of 1 Enoch, which is considered the oldest text of Jewish mysticism, were also found with the Scrolls. Since evidence shows Jewish mysticism existed in the third century B.C.E., as Enoch indicates, then it would certainly have existed in first-century Israel.
Quote from: Jewish Afterlife Beliefs
Here are a few in Hebrew: