I don't know of any web resources specifically about the Singapore region. The FAO species catalog is available as a PDF, but the updated version doesn't have the octopuses yet. The old one that does have the octos is available at http://www.fao.org/docrep/009/ac479e/ac479e00.htm
Other than that, there are a few web sites that cover a few species, but few that are comprehensive, and almost nothing on care. The best care references I know of on the web are the ceph care articles here on TONMO, and they're not going to be specific to Singapore's local species, but a lot of it generalizes to octopuses in general, and we have a number of folks who have worked as professional researchers and aquarists who can often answer specific questions.