As you have probably noticed, Mt. Fuji is pretty far away from Tokyo. Also one item the guides don't really say much about is that the sightseeing bus loops start at 9am. If you take any of the ~6am buses from Tokyo up there, you will be too early for the sightseeing bus routes. Also if you are planning to go all the way out to Motosu-ko using the sightseeing bus then you'll want to work this part out ahead of time. If you are keen on the various sightseeing places (aside from climbing the mountain) without driving, then 2 days one night is probably about the right amount of time.