Went KK last May, it was raining though it was supposed to be the best season. Be prepared.
Do note that there are 2 trails up KK: the Mesilau and the old trail. I recommend the Mesilau trail as it is more scenic (more photo opp!) and quieter. However, this trail is longer and more challenging, so train up before attempting it.
If you cant get enough people for your trip, you might want to consider joining an adventure tour like those by BOAC (http://www.boac-online.com/) We spent about SGD 700+ for the trip which include airfare, accommodation, transport and trekking pass.