It sounds to me as though you may be hopping around a little more than you will enjoy: Oahu, Maui, Big Island -- all in a two-week trip? You plan to divide your Maui stay? Why Kula on such a short stay? (Perhaps that is where your friends live.) If you want to avoid crowds, spend less time Honolulu.
We've spent two weeks in winter on each of the four major islands for over 30 years. Big Island is indeed BIG, if you want to do more than glimpse it; five or six nights would be too little time, IMO.
In winter the northern portionsand higher elevations of the islands are usually cool, windy and wet. This is especially true of Kauai and Oahu, but also Maui and some parts of Big Island too (Hilo, for example).
You might want to post on the general "Hawaii" forum to cover the whole trip you are planning.