In reply to Blizzard:
In Nepal, the season will have an effect on where you can reasonably expect to go, assuming 'normal conditions'.
March-April will have too much snow in, say, Mustang, but would be good for the trek into the Kanchenjunga area which has lots of leeches in Sept. Crossing high passes into the Khumbu may be impossible in early April but a pleasant trek in October. November might be too cold in the remote Api region, but fine in the trekking lodges of the Khumbu.
Three months is quite a long time, especially if you find you don't actually like trekking in the Himalaya. Time is short for most nowadays, so you're unlikely to find partners for the whole thing start to finish. Maybe breaking it up into two or three segments, with some downtime in KTM/Pokhara in between?
Having that much time, you may want to try to do things that you'll never get the chance to do in future years when you may only get three weeks off. So far west Nepal, Dolpo, Kanchenjunga BC etc might be worth looking at. Also, are you interested in Buddhist culture, or don't give a yak's ass about culture and want to climb a 6000m peak? Etc etc...