Yes, been to Bandung, it's lovely. Infrastructure is par for the course, hotels are good not great, and I never used the buses within the cities so can't comment. Not very hard for a tourist to get around though I don't think, especially since everyone has maps and translate on their phones. I didn't struggle in that way and it's certainly not infrequent you meet people who speak English, especially workers in hotels as well as bars and restaurants in high traffic areas.
They do have very bad traffic in parts and IIRC use a system where on certain days only certain vehicles are allowed to drive (depends on license plate number). Honestly, if you want to explore the island, I'd recommend just training it from big city to big city, and sign up for some day excursions if you want to hike mountains, do riverboat/speedboat stuff. The rail system is fine though can be frustrating with some of the security.
I find the magic of that part of the world (Cambodia/Indonesia/Thailand/Vietnam) is 1) geographic beauty, 2) culture of history/food/sites, and 3) the warmth and kindness of people relative to the wealth of the nations. Affordability is great too, and all those attract people moving there. While I'm a bit of a mutt, I come across as obvious gringo there (stick out more as I'm a physically big person) which means at times garners extra attention, but it's more friendly smiles and hellos as I think tourist population is so much lower there than Bali. I remember in tourist areas having kids in school uniforms asking if I wanted to sponsor them and their schools etc.
Java, like the country as a whole but unlike Bali, is overwhelmingly Muslim but very secular, and has a really good vibe (weather great, chill, people friendly) and really enjoyable nightlife - super social. I recall they were like introducing a law of like no sex before marriage, but no idea where that went or how serious the enforcement of that was. Probably something that people in little villages mite be culturally enforced, but I don't think it's mainstream or applicable to tourists. People go out, and it seems like everybody there is a great singer or can play an instrument. So to me it was a super nice mix of fun but without vulgarity. Much better than Bali where the whole gig is bar/hotel/souvenir shop/tattoo parlor/massage parlor aka sex workers; and tourists everywhere.
