There's a lot here to touch on and there's just no one right way for everyone. I haven't had an occasion to worry about armies fighting since I started running 5e, but if I were to do so in the future, I'd use BECMI's The War Machine rules updated for 5e. It assigns a force rating to an army (or divisions of an army) and abstracts things so you can roll an outcome rather than using miniatures or rolling out combat conventionally with large numbers of individuals.World Building Question 2 Army building
So I asked for general DM advise, because hello I am new to Dming. However I would like to start a series of specific posts asking about different parts of world building. This isn't a plus thread per say, but if you think I should not world build that is not very helpful.
Also Warning, I ramble when I am excited even in text.
(if you want to see part 1 https://www.enworld.org/threads/world-building-commerce-and-gold.698360/)
Okay, so wind up to question 2: Soldiers and War
When your games involve wars and kingdoms forces how do you build them?
I have seen DMs build full PCs like fighters Rangers Wizards ect. And then fill them out after that with NPC stats from the MM. I have also seen DMs just take monster or NPC stats.
My personal thought is based on something I found here online. Take the NPC or Monster stats and add 1 or 2 class like features.
However I then worry when is too much too much? Like if I take guards and knights and other NPC stats and add human or elf or dwarf to them, then give them action surge and second wind that sounds like a cool "champion" or "commander" but I would not want a legion of 100 of those (tracking those action surges would be a nightmare).
Then because for my world I am using a lot of Divine magic I started to think about spell slots. I wonder if there is a good way to limit those.
As I am typing this I wonder how much can be hand waved. Like I can call an army of paladins an army of paladins the players don't need to know if they have smite or lay on hands unless they are part of an encounter, and at least at low level those encounters need to be small or it will TPK.
Then I am wondering, do I just story point who wins if I have 2 NPC armies fight, or should I 'roll it out' in between games to be able to tell the players it was 'fair'
I also have seen many times here and elsewhere online that enough commoners can take down a dragon. How much do I need to worry about army sizes?
If I want to throw numbers around as intelligence about 1 feudal lord or another what are sane numbers? Like if someone owns 3 towns and 2 castle/keeps and a bunch of farm land and the DM told me they can field 200,000 troops I would be highly skeptical, but if they have 20,000 is that too much? What about 10,000?
How does caster change this? Like If 1 lord can field 5,000 spear men and 2,000 archers with 500 light cavalry and a dozen siege weapons, but there enemy can bring 400 spear men, 100 archers, 50 light cavalry and 60 level 5+ wizards and 100 level 3-4 wizards and that side has 30 clerics/healers it seems like the casters are a major force multiplier.
Also monsters. Like if one side has ogres and the other side has goblins that skews things too.
Unfortunately, I can't find the converted rules on the web, but I do have the rules and an accompanying Excel sheet that I can up load.