Begin with a Warrior and Cleric guild. Hire a couple of them and then build a marketplace. Some random undead creatures and rats will attack periodically. When you accumulate a bit more money, place a guard tower to the right and left of your castle for added protection.
Nearby are some undead crypts, plague stricken graveyards and sacred ground areas (guarded by elementals). Since you don’t have rangers or rogues, these locations will be uncovered slowly, giving you time to give your heroes some experience to gain a few levels. Be aware that if you destroy any undead or graveyard areas, a vampire will emerge. They are at level 20, so they will not be easy to kill in the beginning of the game.
Strengthen your forces further by building a blacksmith, another Warriors guild and upgrading the other existing guilds and towers. For more gold, there are trading post locations. They are located in the following places: due west of the castle, southeast next to the road (with a crypt nearby), northeast near the road, and the southeast corner of the map.