Istanbul
When I use the Catacombs, do I leave an Assistant there and can I pick up an Assistant at the destination?
You leave or collect an Assistant at the Catacombs as for any place, take 1 good or coffee, then move to any place without taking its action, paying anyone or having encounters. You neither drop off nor pick up an Assistant at the destination, even if you left one there earlier. The teleport is not the first-phase movement.