The NPCs templates found in the back of the 5e Basic Dungeon Master’s Guide and the 5e Monster Manual are a great resource for a campaign. However they don’t cover the range of military types that would be found in a feudal setting.
In the rules there are the Guard and Knight templates with little to choose from in between. The following are a basic set of templates to use in a setting inspired by Medieval Europe during the middle ages.
To me the Old School Renaissance is not about playing a particular set of rules in a particular way, the dungeon crawl. It is about going back to the roots of our hobby and seeing what we could do differently. What avenues were not explored because of the commercial and personal interests of the game designers of the time.
What are RPGs?
A game where the players play individual characters interacting with a setting with their actions adjudicated by a human referee.
Rules are an aide to help the referee adjudicate actions and to help the players interact with the setting.
Dice are used to inject uncertainty which make a tabletop RPG campaign more interesting than "Let's Pretend".
The only thing a player needs to do to roleplay a character is to act if he or she was really there in the setting in that situation.