If you play rogue you will also need Polymorph for skills like Chameleon cloak. Spread your wings is probably nice to for more mobility.
Early one though playing backstabbing rogue will be probably pretty suicidal, probably should bow or crossbow at first, depending on difficulty.
Though not sure if scoundrel is such a damage machine, we used our rogue mainly as a jack of all trades. Archer out damage him by far, so most times he made early damage burst and went invis and later on helped keeping enemies down by applying knock down and finish them off too by backstabbing them.
I loved to play Scoundrel-Aerothurg in the first, but that got sadly totally ruined.
