Yes, you will need to fill in all the possibles. I didn't find much except for a naked pair, which let me at least eliminate some possibles. This is not an easy puzzle by any means, or I was missing something. At this point, I looked for hidden singles. Usually they are made naked by finding pairs and triples, but sometimes not as in this case. Found one that was made a hidden single because of the pair I previously found. Won't tell you which so as not to spoil all your fun unless you ask.