(i'm also struggling to decorate/create my island so i might not have expert advice but i can empathise lol)
which villagers do you have at the moment? are you planning on changing them or are you happy with who you have?
from visiting dream islands and watching countless design videos i've seen that most people either choose to create small personalised areas for each villager (like making themed gardens around each house), or they create one big residential area (such as a boardwalk area or highstreet) and fit houses into that, without theming them individually. so i guess you could try to consider which of these you would prefer to make?
also!! for gothy islands i think theres lots of different things you can do with them - you could maybe make a graveyard area, create some secluded forest patches and maybe put the campsite in a spooky, lonely place. or if you want a more urban-vampire feel you could maybe go for a big city theme? you could also create a cosy area and put most of the buildings and houses close together, and then have the rest of the island feel more dilapidated and unmapped - that could help to create a spooky atmosphere yk??
it def depends on what type of goth youre going for though!! for the trippy aspect, a city vibe might suit u well!! it's definitely difficult to keep that atmosphere while playing though, i'm also going for a gothy island and i only really play during the night, whenever i play during the day it's like a jumpscare bc everything is so bright and un-scary lol
some other ideas for things you could add if you're going for a spooky atmosphere might be black flower variants, maybe even purple or orange, and maybe some more alternative-looking villagers!! (my top fave would have to be Muffy!! maybe Marlo too! or even the more unique villagers like Lucky)