[Firebird]

1) the limits are low and as Nyorin stated you would not want to drive faster on some of the smaller roads. People do usually drive faster than the limit. I haven´t seen a speed control in my month driving in Japan bu i didn´t risk beeing fined because i don´t know how much the fines are. I guess go with the flow and keep the limit in high traffic areas on the outskirts of big towns.

2)I have only been on the highway once so i don´t know. Highways are expensive so i tried to avoid them.

3)My license was translated in like 2 hours but my situation was different. I got my original license stolen and had sent a new one directly to the ambassy, the day it arrived i could pick it up with the translation, so i guess there are ready to print quickly. But i´m not 100% sure how long you will have to wait. I´ve never gor checked by the way (but i wouldn´t want to drive without either).

4) There are traffic jams around the big citys during morning and afternoon rush hours and during Holidays. Anywhere outside the huge citys i didn´t have problems (even Hiroshima was ok). Generally i´d say you should be alright.