I was just reading about another trail: the High Sierra Trail. Its general direction of travel runs perpendicular to the JMT, and crosses the Sierra instead of paralleling the summit. It's much shorter than the JMT, only 50 miles, but it has less red tape and is a major journey because you pass over the major subranges of the Sierra. You can easlily get permits a few months out, unlike the JMT where you might have to wait years to get one.
It's also the road (trail) much less traveled. If you don't like crowds this could be a good start. I want to try it in September.