Sorry, haven't read through the rest of the thread...
The novel after the WIP is going to be a third-person moving multiple PoV - the first time I've tried it in a novel. I've realised that I need to find a voice and point-of-view for my narrator - 'the author', if you like - even if they're not a character, or at least a character in the book, although how opinionated and how like me they'll be I don't know. I'm playing with various ideas about where this narrator stands in relationship to the story they're telling, without it seeming tricksy.
It's worth remembering, though, that just writing from an MC's PoV is no guarantee that your reader will care about them 0 they need to engage us, and sometimes a view from another character might do that better.
When I think you need to be very sure about is why you're moving, when you're moving away from the main one or three PoVs.
I realised this recently, working on a report of a novel which was very much the story of a single man's life, as a microcosm of a particular moment in history. In the first version I saw, the PoV switches were all over the place, often just when I was beginning to care about him, or just when his internal demons were driving him to do something drastic... The crude solution for a muddle like this, which almost destroyed the narrative drive, would have been to tell the writer to stick to a single PoV: it would have been a quick fix, and I've heard the advice given loads of times. But this man had a public aspect to his life, so how he looked from the outside mattered. And he wasn't a very introspective type, so too much brooding about the disjunction between his inner and outer worlds just didn't work either. So I didn't tell the author to do this, but to really concentrate on why and how and when he switched: that what we were shown from outside was always something which we couldn't know from inside, not just from the plot point of view, but because it adds depth and drive and complexity. And it's worked, though it wouldn't be fair to go into details.
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I think what I'm saying is that if you really, really know why you're switching, and it's not just 'in another part of the forest', then you'll probably take the reader with you well enough. If we're jumped to the nother part of the forest, then we need to be made to think, look, guess, about how they connect - to keep us turning the pages to find out. So we need to be given enough handholds about what the connection is to keep that going.
Maybe it helps to think in terms of the old 'what does she want, what gets in the way?' idea. It's a while since I read it, but as I recall, in H&M, Rosy, there's a really strong sense at the beginning of the conflict-in-waiting as all the parties begin to converge, which keeps us reading through quite long passages of separate activity.
Oh dear, I don't think I'm making much sense - I'll stop now.