40 Kittens
The killer in me
Having re-watched a lot of the season two and three episodes on Sky quite recently, I'd say that Joss probably had little notion of Willow turning out to be gay until at least the appearance of vamp Willow. For the better part of the first three seasons, there is pretty much no indication of her being in any way a lesbian. I'd say that it was a later idea that quite successfully worked with what was already established.