score:6
Finland, Denmark and Iceland are all part of the Schengen area, so you will have to clear immigration in Helsinki. While for some reason FinnAir do not list a minimum connection time for non-Schengen to Schengen flights, the worst MCT they do list is 75 minutes. Given you have more than twice that time in your connection, you should not experience any trouble in making your connection, assuming the inbound flight is reasonably punctual. Furthermore, I gather the standard non-Schengen to Schengen MCT for Helsinki is just 40 minutes, and you have over three and a half times that.
If you do miss your connection due to circumstances outside your control (e.g. a late inbound flight), you will be rerouted by the airline to your final destination (i.e. Iceland) and provided accommodation if necessary, provided that you book all your flights on a single ticket. This will be the case, for example, if you book your entire journey at the same time on Finnair's website.