Villages first for a less crowded and easier on Teeth environment, minimizing false positives, then slowing going more and more urban as long as Teeth behaves herself. I'm honestly more interested in working with Teeth than successfully finding problems.
Village witchhunting it is. Ignore the fact that I'm literally a xenos witch.
From what the two of you have gathered from long months of living with the Warriors, their typical way of dealing with heretics is to immediately start shooting once you are sufficiently convinced your target is an Ancient of Chaos. Not that you saw any of that happen first hand, but they where certainly proud of the times they saved the world from Chaos by transforming a suspected cultist into dinosaur chow. As such your witch hunt needs no authorization, so long as you have sufficient evidence any killing is unlikely to even get a show trial. "Sufficient Evidence" of course depends on the status of the cultist you just ventilated.
Using psyniscience feels odd on this planet. At least for the human. It is as if the planet itself is a psyker. One powerful enough to be felt no matter your location. Still it is the fortress that burns brightest, like a miniature astronomicon just for you. There are smaller beacons elsewhere in the world, with the same feeling but less intensity. Like a match compared to a lighthouse. While these may not be the light you're looking for they may have attracted their share of moths, given what you can piece together about what the light is.
Cross referencing with your map, one is in a wreckage of a void ship that has been transformed into one of the larger villages on the planet. Another is deep within a jungle, on a mountain within riding distance of three smaller villages. The last promising light is underwater near the shore by a medium sized village. Still this light is clearly that of the planet rather than that of an invader, it is possible all of these places are free of Chaos Taint. Perhaps these may even be the safest from such forces, should the planet be working against them in its own subtle way. By a more mundane search you have the frequencies given to you long ago (and a few more you picked up during downtime planetside). While your sources of potential information are heavily controlled and filled with propaganda, you could likely piece together villages that have a higher rate of disappearances, crime, or "triumphant victories over the forces of Chaos". Such places are also likely to have non-chaos related violence issues to work through even if their issues are not being directly caused by the warp touched.