looks like you have bit of space there sooo...
change the fence style; you can also customize it to whatever color that you want and add items that youve also customized to be close to the same color. not everything, just a few tidbits here and there. a few flowers and bushes wouldnt hurt.
across the river/pond/lake there lol
if you want a volcano, then make sure you have cool things around it, trees/bamboo/palm etc with decor...maybe a few tiki torches, the kettle pot, bamboo, a couple of fruit trees, houses etc. always have room for a path.
it depends on which way you want to go, because you also have industrial on the right hand side, and if Thats the case then you should go full on tech stuff *also in the residential center* along with the space items etc.
ive never seen an excellent island thats had a combo of themes well...have you? if so please pm me and let me know! i wanna check it out