I have a PS Vita 2000 running 3.55 and wanted to know what can i do with hacking a ps vita? if i need a lower FW can i downgrade and what FW would that be?
No, you can't downgrade the vita at the moment unfortunately.
But if you have a PS3, you can activate that 3.55 Vita by buying Mimina Lyar Chronicles and transferring it to the Vita. And at the same time, you can download an exploit savedata for Mimina and install either a TN-V bubble or an ARK bubble to the home menu using that exploit savedata. These bubbles load PSP and PS1 backups and homebrew, so no Vita piracy yet.