Questions about the Septuagint

Hello, I have a few questions regarding the Septuagint.

Firstly, was the Septuagint an accurate translation of the Tanak for the time period?

Secondly, is the Septuagint Christian’s use today an accurate copy of the original Septuagint?

Thirdly, are there any Hebrew bibles/scripture predating the Septuagint which significantly differ from the Septuagint?

Thank you all.