There's also a possibility that when you get here you'll have to pay nothing up front because the apartment is taken out in your BOE's name and has been for years. I paid no key money, didn't have to pay rent until I'd been here a month, and since the same apartment has been in use by the local ALT for over a decade the place was already stocked with good stuff above and beyond what the BOE provides by contractual obligation (in my case, vacuum, stove, fridge, bedding, TV, dvd player). I didn't have
to buy anything, which was great because my dad died in the middle of June and the only reason I was able to scrape up even $1000 was that my mom had some savings she could loan me. I also got paid right on time less than three weeks after I got here.
This won't necessarily be what you get, of course! But it's possible. Honestly, I think if you just relax and take it as it comes then you'll be fine.
Oh, and my predecessor made sure I knew what I was getting into. In the wake of the 3/11 disaster and concerns over the Fukushima power plant, placement announcements were delayed because the US and Japan were politicking over placements outside the Japan-regulated evacuation zone and the US-recommended evacuation zone, so I didn't get my mailed contract and letter from my predecessor until mid-June (ironically, less than 12 hours before my dad kicked it,
). The contract told me exactly what my CO is responsible for providing at my apartment. Between the letter my predecessor sent and a two-hour Skype conversation I had with her, I knew before going how much I was paying for rent, that I had no key money OR deposit to pay, and a variety of other good information about the town and work.
Current ALT in rural Hokkaido. Hails from Alaska, USA.