I don't think Tolkien took Elves from Finnish mythology. I'm not very knowledgeable about the subject myself (
), but I think Finnish myths mainly tell of shapeshifting trolls that and tiny gnomes/elves as local spirits that will reward good deeds (and food left for them) with good luck.
However, there is one story in Silmarillion that is clearly inspired by Kalevala. The story of Turin has similarities with the story of Kullervo, the hapless. Song of Hiawatha, by American poet Longfellow, is written in English but using the style and rhythmh of Kalevala. It might represent the style better than the translated Kalevala.
EDIT: I'd rather have Middle-Earth total conversion instead of few out-of-place nations. And I think a tutorial would help much more than familiar-seeming nations.
