Coming back for the expac

I used to run an ethereal knives build

Can i still change my spec nodes so i can keep playing this character or do i need to find a new build (if so does anyone know of one that's of a similar playstyle and that uses similar skills so its not very gear expensive for me to swap to?)

You don't have to start a new char. You should have a full respec on your current char. With the upcoming expansion you will get another full respec.

EK should still be ok in the expansion.