Question on Sprite Management in a 2D Isometric Game

So I'm relatively new to game art/development and I was just wondering what's a ballpark estimate for the number of sprites/sprite sheets for games? Also, I was wondering how expensive it was on the unity engine (or game in general) to call multiple sprite sheets for each unique monster?

More details:
Currently, I'm working on just the "monsters" (no other NPCs just yet) and the counter is already at 19 different monsters, some of which are just colour reskins. Is it a safe decision to make a sprite sheet (2048px x 2048px) for each individual monster? since the game is an isometric game, I've got 8 degrees of movement to animate for both moving and idling plus any aggressive stances I may add in later on. Some quick number crunching puts me at 168 sprites per monster to cover all possible stances it would need.

Spritesheets is the obvious choice over individual sprites for fewer drawcalls, but I'm now interested in how many sprite sheets is typical of games, cause this is sounding somewhat high for me at this point. Designing them isn't the issue (I've got a system to make the sprites relatively quickly set up), just want to make sure I'm not digging myself into a hole on the programming side of things.

My game will launch on PC initially and transition to Android/Switch in the future by the way, as I'm sure that will affect the answers.

TL;DR:
1) Whats a rough estimate for the number of sprites/sprite sheets on games? I know the range will be huge, but just want to know a ballpark estimate to see if I'm pushing any boundaries (lower or higher end).
2) We all know that sprite sheets > individual sprites, but should I do individual sprite sheet per monster or one huge monster sprite sheet?
3) How expensive is it on the engine to call up sprite sheets for each unique monster?
Bonus question: What your go-to sprite count for a walking/moving/attack animation on a 2d game?

All very basic questions, but surprisingly enough, Google wasn't throwing me the information I need for this.

Thanks in advance!

 

You should take advantage of Unity's SpriteAtlas system. It will tightly pack your designated sprites into a big texture, getting rid of any wasted space in the sprite. Using that system you can have individual sprites or spritesheets, it doesn't matter.

Number of sprites and sprite sheets in a game largely depends on the game. There isn't really a ballpark estimate because depending on how animation intense your game is, what resolution the sprites are, and how efficiently they can be compressed, how many have to be in memory at the same time, etc, all makes a huge difference to how many you can support in your game.

Ideally you would aim to only pack sprites together that are commonly viewed at the same time, so you're loading as little unused texture space as possible. You wouldn't want to pack a boss monster along with monsters that never show up with it, because then you're loading data for the boss sprites anytime you load the other monsters and vice versa.

Another benefit is draw call batching. If two sprites are using the same material, and the same texture, they can be drawn at the same time in one go. A spritesheet/atlas is a single texture, so you can have many monsters batched that way.

 

Okay, so just to clarify; saying I'll need upwards of 6000 sprites just for basic monsters isn't crazy talk then? I'm thinking I'll have each monster and it's relevant sprites in one sprite sheet (around 160 sprites) so that it's as efficient as possible since each only has a small spawn chance and not a guaranteed chance.

 

Anno 1602 (Also known as 1602 A.D.) has around 55000 sprites for reference. But it also has every sprite 3 times in different resolutions for different zoom levels.