I play Corsairs for SBG, havent played many games of WOTR so can't comment on that.
For SBG I use a singe captain, and then equal numbers of spearmen, shields and the guys with crossbows (arballesters?). If I canI get a horn in there to boost my courage.
With F4 and a 4+ shoot value they're awesome, especially as everyone comes with throwing weapons!
Don't bother with normal archers.. order some Dark Elf crossbows from a bits site and convert the archers into crossbows. For a couple of pts more, you get Defence 6 against shooting, and a crossbow, making them one of the best shooting models in the game (for me anyway).
In my 500pt army I have one captain with a crossbow, 16 crossbows, one with a horn, 16 spears and 16 shields, and then one random corsair with spear and shield to sit with captain. I use them in groups of 8, dancing around throwing their daggers and shooting with crossbows, once they're softened up I then charge in and mop up the survivors. And don't be afraid to shoot into combats with the crossbows, I've stopped many heroes calling heroic combats and getting kills in Contest of Champions by "accidentally" shooting my guys
Your biggest worry will be shooting.. with a low defence bows will start racking up kills quickly, but you should always be hitting the model limit in games, so you can afford to take a few casualties.