Short answers, pulled from the story.
The first hostilities between the Finnish Army and the 20th Mountain Army took place on the 28th of September 1944. The war in Lapland concluded early November 1944 after Germans withdrew from north-eastern Lapland at Karigasniemi on the 25th of November 1944.
Fire spread beyond government buildings destroying housing in Rovaniemi after a train loaded with ammunition caught fire at the railroad station on the 14th of October. The explosion spread throughout primarily wooden buildings of the town while Germans left mostly scorched town to Finns on the 16th of October 1944.
Finland experienced 774 killed, 262 missing and around 2,904 wounded. Germany suffered around 1,000 deaths and 2,000 wounded with 1,300 German soldiers becoming prisoners of war handed over to USSR.
German withdrawal effective by November left Lapland systematically destroyed according to orders from Lothar Rendulic. A strict order issued on the 6th of October classified only military sites as targets for destruction before extending to all governmental buildings except hospitals on the 9th of October.
Soviet reconnaissance troops met with Finnish Army at Ivalo by the 5th of November. Soviet troops stationed in Ivalo did not leave until September 1945.