When I did my "big" tour and return to Uni, I started planning all that in February, and finally hit the road at the end of September. I chose the end of September because of an event I wanted to ride held at the end of October. That gave me a month to cycle from Sydney to Melbourne for that event.
Usually my tours surround events or have to fit into work/school schedules or have to work with the seasons, so I have a pretty good idea when I'm going to travel months in advance, and I can start making plans.
As for checking the gear, that's what weekend tours, in advance of the big one, are for.
Have a look at this thread I started recently ... it may give you some tips:
http://www.bikeforums.net/showthread...-Extended-Trip