I will answer the 2nd question first. Yes, Job is considered the first book in the Bible because the book is set in the ancient days of the patriarchs, before the time of Moses.

Job was a prosperous man whose life resembled that of Abraham.

His longevity corresponds to that of the patriarchal time, he lived 140 years beyond the main events of the book bearing his name (Job 42:16-17).

There is no mention of Moses, the Law, or any other event or institution of the Jews . . . . Job is dated by most scholars at 2000 B.C..

The book of Malachi bears the name of the prophet Malachi. Malachi dealt with much the same problems as were prevalent during the time of Ezra and Nehemiah.

Most scholars believe that the book has its setting in the interval between the two visits of Nehemiah to Jerusalem. Passages in Malachi and Nehemiah show that much the same problems were considered in each book.

From about 606 B.C. many of the people of Judah were carried into Babylonian captivity. After 70 years, about 536 B.C., about 42,000 Jews under the leadership of Zerubbabel returned to Jerusalem.

Then under the leadership of Zerubbabel, the governor, and Jeshua, the priest, the work of rebuilding the Temple was begun. However, the work of rebuilding soon stopped because of the opposition in the land.

After the work had been stopped awhile, Haggai and Zechariah encouraged the work to begin once more. The Temple was rebuilt about 520-516 B.C.

Then about 60 years later (around 457 B.C.) Ezra had come from Babylon to Jerusalem to help encourage and reorganize the nation.

Then, about 13 years later (around 444 B.C.), Nehemiah came to Jerusalem and directed the rebuilding of the wall. This seems to have been close to the time of the conditions and events described in Malachi.

But actually, the last Old Testament prophet was John the Baptist, who lived and died before the cross of Christ, and who's teaching was to direct the hearts and minds of the Jews of his day back to the Father.