I'm building up an Eldar war host myself and also started with the Battleforce(I know it's pish). I will be getting a Farseer and a Warlock bodyguard, that's the basics done, The Banshees are useful at taking down heavily armoured troops but really need a Wave Serpent to get them into the thick quickly as they don;t have the best ranged weponary, I will be looking at expanding the Dire Avengers up to 10 as a troops choice who can also pack a punch they can hold objectives and hold their own. Definitely add a Fire Prism, this tank is just awesome, one of if not the best in the game.