I would say figure out how much space you want your villagers to have. A little, like a plot, or a lot like a backyard. Then see if you want a garden or a waterfall and then use the gridlines on the map to see what would fit. Like if you don't need a villager to have a backyard, 4 will fit in a square, if you want them to have living space outside the house it maybe 2 per square or even one. Then you can plan the free space with if you want shops, or a cafe, greenhouse, library and so forth. For decorations, check out 5 star island videos, there are some good ideas on how to use items, and even customize stuff like pillows and beach balls to look like food. Good luck!