As someone who lives in Bandung part of the year, I’d strongly advise you not to visit on weekends or holidays. And do not, I repeat, do not, drive there. The train is fine.

Going mid week is fine. Angklung is fun, and there are cool things to do outside the city.

If you have more time, Yogyakarta is a nice trip. 6-7 hours on the train each way. My wife and daughter went last month, and some really nice activities off the normal ones you see people doing. I’d do this as a 2-3 day trip, though.

You can often find a car with driver for $30-50 per day. Trains can be fine. Buses and shuttle buses can be hit or miss.

I don’t really recommend driving your own car here. While it’s not really dangerous, if you get in an accident, there can be mobs of people who gather and dispense “justice” if they think you’re trying to escape without paying, or lord forbid you hit a kid.