Is the finnish word kupla related to italian world cupola?
No, it is not. According to the Finnish etymological dictionary the word “kupla” is related to other closely related Finno-Ugric, especially Baltic-Finnic languages. The meaning in all these languages is more or less the same as in Finnish, i.e. rakkula, rakko, vesikello (follicle, bladder, blister, respectively). The word was first mentioned in additions made by Henrik Gabriel Porthan in 1770s to a dictionary originally compiled by Daniel Juselius.
Source: Häkkinen, Kaisa: Nykysuomen etymologinen sanakirja. WSOY 2004.
Additional information on Baltic-Finnic and Finno-Ugric languages: