You can rest in a bed, etc; there are some sleeping mats in the army tents close to the north gate waypoint, some in the (not quite as convenient) Hall of Heroes, and usable beds in several houses.

Jahan starts with a healing spell, and it wouldn't hurt to have one or more other party members pick up some (Regeneration and later Water of Life [water], Cure Wounds [warrior], First Aid [ranger]...) and you can also use food.

If you talk to the legion commander, get permission to enter the crime scene in the King Crab inn and then do so, you will have to walk near/past 2 of the other companions. Explore around town enough, and you can find an area with some combat suitable for level 2 or 3, as well as the last companion.
Madora, a 2 handed knight walking around the Kick Crab bar
Bairdotr, a ranger locked in a cage outside the legion headquarters
Wolgraff, a scoundrel in a set of tunnels under Cyseal, with multiple entrances in town, and one just outside

There is experience available in town from quests and exploration. Another companion should help with combat, and when you leave town, the easiest direction is out the gate behind the King Crab (the only one open, that you don't need to talk to a guard to be able to leave).

If guards see combat, they will come out to help, though can also get in the way of where you are planning to use AoE effects (the magic ballista on the walls are also usable, if combat is close enough).