Should I focus on getting as much flawless as possible or would it be worth more to skip a few fireworks for combos?
Great question!
The answer is that it depends on the level and timing of the combos. I usually tell people to focus first and foremost on getting as many flawless possible. After that, try to think about the combos. In the higher stages/levels, the combos are worth a lot of points, so sometimes it's perfectly fine to ignore the flawless and go for the combo. I'll still be working on the timing of some of those combos, because some of them take planning, but that's what I do in general.
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For those who haven't seen, I've updated some of the questions to reflect the changes from the last MyVMK Update. Those questions are marked as "UPDATED" in the OP.