Of the three types of warriors, fighters certainly present the fewest problems. In a Viking campaign, the bulk of player characters should be fighters. Vikings were known for their warlike spirit and ferocity. Any player character with appropriate ability scores can choose to be a Viking fighter.
All fighters must initially be proficient with either the broadsword, axe, or spear. Additional weapon proficiencies can be chosen as the player prefers (provided the weapon is available in that time period and place). Upon attaining 9th level, the Viking fighter can attract a body of warriors. However, instead of using the tables found in the Player's Handbook, the number and types of followers attracted are listed below.
To use the tables, roll once to determine the lieutenant, once for the regular troops who come to serve and once to determine the type of special guard who attends the character.
60 infantry w/leather armor, shield, and sword; 20 archers w/leather armor and shortbow; 20 infantry w/ chain mail and battle axe
26-50
50 infantry w/leather armor and spear; 50 infantry w/chain mail and battle axe
51-75
40 infantry w/studded leather, shield and sword; 20 infantry w/chain mail and sword; 10 cavalry w/chain mail and spear; 10 archers w/leather armor and shortbow