Widerĝe has an explore Norway ticket that allows unlimited flights within a certain period that you could check out: http://www.wideroe.no/en/tickets/explore-norway-ticket - and then see several more places.

And instead of visiting several cities, if I were you I would rather spend a night or two for instance in Lofoten staying in a fisherman's cabin (rorbru), either flying or taking the Hurtigruten ship through some of the really narrow fjords in that region.

The central part of the country is beautiful to drive across (Oslo - Bergen), but that requires several days and a car, so taking the train is definitely a good idea!