I'll take a stab at this as someone who lives here. >>28
hopefully by the time the JET is over, I'll either have found a permanent job to keep me located there
JET forums are filled with miserable posts. JET teachers have been persistently considered as expendable labor to the government and long-term contracts are becoming increasingly rare. Teachers are notorious for being overworked to the point of essentially living at their schools so securing an English position isn't very alluring. They're more overworked than nurses and definitely more than your average salaryman.
They are not me, I am not them, and I have no idea what mentality they had/have when living in a different culture.
Who you think you are does not matter to Japanese society.
Most renting agencies won't talk to you if you're not fluent, nor would many renters consider giving a room to a demographic notorious for making noise, throwing trash away incorrectly, and constantly inviting people over. Prepare to be turned down often. All the paperwork is in Japanese. Downpayments alone will reach $3000~6000.
If you look like a foreigner you will be regularly stopped by police. If you don't have your resident card or passport it's off to the station. If you don't have a visa you'll be deported. They have the right to pat you down and go through your belongings without any justification.
Japanese employers look for new hires seasonally on a very rigid schedule: New uni grads for top-tier companies, those switching jobs, then the rest. The majority get hired right away after graduating and if you're not within this demographic you're already considered second-tier. The system does not make concessions for foreigners. The applications, interviews, and contracts are in Japanese. If you're not fluent you're useless to any company worth working under. Second-rate companies don't offer commuting/housing stipends, visa assistance, your income will be less than $25k a year, and they will have no problems giving you 60+ hours of overtime. Even normal salarymen regard their apartments as little more than hotels to sleep in. Come home at 11pm, wake up at 7am.