Returning player (Thief)

Hello guys,

I left this game more than 2 years ago because I was bored.. I have a thief which was full stuff and everything.

Now with the new extension i want to get back but I don't know where to start..

-Is thief still OP on PVE and PVP ?

-Should I reroll for an other class ?

-What's the faster way to lvl 80

-Which classes are the most OP, any class rank ?

-Any spot to farm gold ?

-Different ways to get ascended stuff ? And how much does it costs ? (If crafted)

I may have other questions later but nothing in mind right now, thanks in advance for your answers !

P.S : sorry for my poor english :D