whoa be prepared man for Japan winter  it was brutal last in Osaka in Feb, i think 0-2C most of the time even in city

for the accom it depends on what type your gang will be focused on? for my case accom at places i visit are just places to shower, sleep, keep luggage, so i dont spend alot on the best looking or most comfy. i will be out like almost 12hrs daily, so its a waste if book nice hotels

as for which suburb best to stay, pick those near train stations or those near your main base of travel. like for eg. if you plan to tackle Shibuya the most, find accom around there or within a station or two away from there. youll thank me when you need pull luggage over roads for 30mins searching where is the stay haha. japanese addresses can be very confusing