Because "todella" is before the adjective "kaunis," meaning it's describing that word. If it was describing the verb, it'd probably be "Suomi todella on kaunis maa." It's an easy mistake to make, but that's learning new languages for you.
'Maa', if meaning 'Earth' (planet) should be capitalized; it is a proper noun. Same with Aurinko 'Sun' or Kuu 'Moon' (Earth's natural satellite). However, Finnish uses capital letters considerably less than English does.
Yes. But as the root word is "tosi" (meaning: "real", "true") maybe better to say that "todella" = "really", "erittäin" = "very". But this is very fine semantics. Especially as "very" also comes from Latin "verus", meaning "true" :)