Most fire fighters start out of high school, so a college grad fire fighter has the awkward start of calling colleagues younger than him with more experience senpai, while possibly getting better pay. The way out of that is to take promotion exams so you're in command ranks.
I think you know about fire fighter ranks. Since the fire department is a municipal service, the top chief reports to the mayor. I think in the US, there are 5-star chiefs, but in Japan, the ranks top out at 4 stars. Tokyo is an exception with a fire agency whose jurisdiction is the whole prefecture.
Each fire department is probably different, but a typical schedule would be 24 hours on duty, 2 days off duty, repeat. A shift would typically start around 8am. If there's no alarm to respond to, the day would be consumed with meetings, inspecting equipments, and training. It is very similar to a US fire fighter's day, with likely similar work culture.
One big difference at a Japanese fire department from a US one is that the ambulance is also at the fire department. So the ambulance driver and EMT are colleagues with the fire fighters under the same roof. The emergency call number is 119 for fire and ambulance. Police is 110. Every kid knows that, but adults forget.
You also wanted to know about Japanese fire fighter pay. It's likely different between a small town fire brigade fire fighter and a Tokyo fire fighter, but a high school grad might have a starting monthly salary of 150,000 yen, while a college grad might have 200,000 yen. A college grad tends to get higher pay raises and earlier qualifications at taking promotion exams, so a high school grad would be forever playing catch up, when it comes to pay.