These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
One more wrinkle about the rhythm: the oral tradition that Lönnrot was drawing from, the last two syllables of each line are sung for about twice as as long as the others. The effect — which Sibelius preserves in his crowningly awesome Kullervo — is quite markedly different from the Longfellow version.
Maybe not just Lönnrot: it's possible that it was meant that way from the start and was the whole point of the story. It is portrayed as quite a nasty situation from Aino's point of view: the cowardly brother selling her out, the mother happily complying in hopes of a powerful son-in-law, and the old and lecherous husband-to-be.
Yes, but that's okay, because she preserves her virginity and honor by drowning herself.