Ugh. Just go for harem, man. It's in the freakin title. However if they build it up from here to him getting an epiphany that harem route is the way to go, then it's all good. If he's too preoccupied with classic modern sensibilities then just have your weddings in Himelda's country...
Though going for anything "realistic" should have been tossed out the window already the moment Reiji met the possible personification of Gaia... so again I say, go for harem.