Are there leveling rules for each MSQ section i.e. finishing ARR and being closer to lvl 60 than to lvl 50?

There aren't strict rules but generally you should be naturally the expected level based on if you have Road To x0 buff. For ARR typically if you have the server xp buff you end up around 56-57 I think. Without it, you have to do some extra leveling before you're high enough level to get to Cape Westwind, and by the time you're done you end up around 52-53.

If you're higher than that, for ARR you'd probably be fine, though if you're moving on to HW and you're starting off at 60 for example, that could be an issue.

Awesome thank you for answering my question.