A common question we get is how many players, plugins, and/or mods a single server can handle. There is no easy answer to this as there are thousands of variables that can affect the performance of a server. However, there are some general rules that can help you decide what server package will suit your needs the best.
1. The Basics - RAM (Memory)
Every Minecraft server has some RAM amount allocated to it which will affect almost every aspect of your server's performance. The general rule is that the more RAM you have, the more players, plugins, and/or mods you can have.
2. Player Slots
The amount of players your server can handle is dependent on how much RAM you have. You'll want to consider having about 50MB of RAM per player on your server. This amount can go up if you have plugins that directly interact with the players.
A good rule of thumb to follow is about 50MB of RAM per plugin you have (some bigger plugins may use more RAM such as multi world, logging, or map plugins).
4. Mods and Mod Packs
View the guide here for rough recommendations/guidelines for modpacks.
You want to run a server that can handle 10 players and 10 plugins. Following the rules listed above, you'll get the following:
10 players x 50MB = 500MB RAM
10 plugins x 50MB = 500MB RAM
500MB + 500MB = 1GB of RAM (Spider plan) required to have a server with 10 players and 10 plugins
Remember: These are all estimates. Nothing with Minecraft servers is set in stone as even slight version differences of Minecraft can affect all of the above recommendations.