Was a residence already prepared for a Monarchy? What was the official residence of the King of Finland going to be, are there any pictures of it?
Yes, it was ready. Now it´s the presidental palace.

More info, history, pictures, virtual tour etc. (in english)
http://www.president.fi/englishWhen Finland became independent (on december 6. 1917. Russia´s bolshevik goverment recognises Finnish independence on december 31.), finnish goverment decided that Finland is republic country. At the end of January (1918 ) goverment forces, known as the Whites, led by general C.G.E. Mannerheim, start to disarm Russian troops still stationed in the western finnish province of Ostrobothnia. At the same time, left-wing forces known as the Red guards, inspired by the bolshevik revolution, seized power in southern Finland. The ensuing conflict between Red and Whites (known also as a civil war, a liberation war, a class war etc.), depending on political views, ended in victory for the Whites.
After civil war the right wing though that republic form of goverment was too uncertain in young Finland. So in October 9. Finland became constitutional monarchy (based upon the instrument of goverment of 1772).
Finland wanted Emperor Wilhelm II:s son Oscar to be the king of Finland, but Wilhelm didn´t let him go from Germany. Then the parliament chose Friedrich Karl Ludvig Konstantin von Hessen-Kassel (Frederick of Hesse), the brother-in-law to Wilhelm II, to be king "Kaarle I" (Carl I), or May be "Fredrik Kaarle".. One used finnish name is Väinö I (George I), but some reason experts doesn´t like to use that name

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Titles: The king of Finland and Karelian
Duke of Ã…land Islands
Grand duke of Lapland
Master of Kaleva and the North.
Well if we want a litte bit imagine the situation... If Frederick should has crowned.... He died in 28.4.1940. His oldest son Wolfgang (1890-1989), "the next king", really was here in Finland. He was the officer in Lapland (1941-1943) when Finland was in war with Soviet Union. Wolfgang got married twice, but he didn´t have any children.
So the next king should has been Wolfgangs eldest nephew Heinrich (1927).. I´m not sure is he still alive. But because Finland doesn´t have king "Henrik I" or "Kaarle III", he was very famous art painter and set-builder, even in La Strada opera. Heinrich doesn´t have children neither, but may be his nephew Phillipp should be our crown prince or king now.
But he isn´t, because Frederick abdicated the thorne in December 14. 1918... Without setting foot in Finland... But yes, we have a nice president now Â


Frederick

And his wife Margaretha. Wilhelm II was her brother.