When you first enter from the west just head west to the waterfront. There will be an ambush by Golems here.
Once you've dealt with the Golems head into the building in the farn northeast corner of town. Corie is sitting in here. She has a little bit of useful information as long as you don't ask her about the green stuff around her mouth. Stoners apparently don't like having their habits pointed out to them.
Wandering around outside in Mernia is Sydow, who sells healing spells, and provides healing herself. The Divine Restoration in particular is a nice spell to get.
Just to the west of where the Golems were is the common armorsmith, and that's about it for Mernia.