It is a survival game with a VERY minor story, I think they started moving away from doing stories instead of focusing on mechanics and porn parts again after Koikatsu, maybe the people they actually listen to, their Japanese customers, didn't care for having an actual story when Koikatsu came out, so they toned the AI Shoujo story down drastically to give it the more sandbox feel of older games, but left in the little story that exists because it was already planned and was a major part of the design despite how little impact it has.
As for the end, yes, the housing island is the last part and, no, there will be no more additions to the game as far as places or story, though who knows, they might have a second game in the pipeline that will be compatible with AI Shoujo characters like Honey Select 2 is. The possibility is slim, but it is there.
As for finishing the game without sex, that is entirely possible given how the AI works in this game. They might ask you for it every five minutes or they may never ask, leaving you to have to start it if you want it.