1. It is really freaking COLD this time of year, you have to Google Mt. Fuji climb and read and read, people will tell you, its COLD AT THE TOP and WARM DOWN BELOW, so that requires extra gear and such.
2. Get there early 4AM is best, and plan on getting home that night, / leaving really late, it takes a whole day to do the full climb.
3. Buy a walking stick there and make sure you don't goof off too much; you want to get to all the stations that will BURN INTO THE WOOD OF YOUR WALKING STICK each stage of the walk you made. To get all the stations in one day is really hard; I hope you are in good shape.
4. Bring money, lots of money, the little shops along the way are very expensive, unless you plan to pack, and CARRY food and water, I suggest you DON'T because it is a bitch of a climb and all that food and water is heavy.
5. Don't eat too much along the way, it will slow you down.
6. Take a camera, (I'd take your least expensive one) the trip can get very wet!
7. There are a lot of people making the trip, you'll have no problem just joining / tag along with a group of people, but be careful; they may have another return route, or go slower then you want. I liked being ALONE on the hike, but within shouting distance of someone.
7.a IF you get hurt, SUCKS TO BE YOU, medical evacuation costs a lot of money, and takes time, be careful!
8. MAP! Follow the map, buy one and make sure EVERY TIME you take a turn KNOW where you are, we ended up 6 + miles from out start point and it was dark and had to take a cab to our car.
9. IF you get lost, know how to say and point out on your map, WHERE your car or start point is, people will help you.
10. NO you don't go all the way to the top, you get to the snow line and turn back, otherwise, you better be packing camping gear and lots of dry clean clothes.
11. Learn how to say "Excuse me" in Japanese, you'll say that about 10,000 times along the trip.
12. Don't lose your walking stick, and if you want you can sell it on e-bay.
13. Wear comfortable shoes that are broken in (used) take foot powder and dry socks just in case in your BACK PACK.
Well that is all I can think of for now, Oh yeah CHEMICAL LIGHTS (Light sticks the you use for diving) AND A FLASH LIGHT !!!!
Good luck, post some pictures when you get back!
Peace!