I'm currently on my 28th long rest in the game (I've been creating a save each "night") and am currently some way through act 3.
I try to save long rests for times when they make some kind of story sense, and once it feels like I've accomplished enough for it to feel as though I've had a full and productive adventuring day. That's of course subjective! It does usually coincide with running down on spell slots, but I also try to ration spells and supplement with use of scrolls, grenades, special arrows and potions to stretch things out when I think that makes more sense.
Given that progression of companion quests seems to be linked less to long resting than it was in EA, at my resting frequency I've found that things tend to happen most but not all nights, so it doesn't feel either that there's a ton of stuff queued up or that nights are too uneventful. And I'm not sure if I've had any issues with quests timing out, though in Act 3 ...
... the quest to find Zevlor did auto-complete with me not having found him, so I'm not sure if that timed out or if I just moved the story on too far. And I am rather worried about Ravengard, given Wyll didn't sell his soul for his location, and I don't know where to find him. Obviously I could google, but I'm trying to do this run as spoiler free as possible!
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Overall though, I don't think there are any obvious right and wrong answers as to how often to long rest. We can each decide what works best for us.