Limits

The server has limits on certain things to prevent lagg and server crashes.

Redstone limits:

Fast redstone clocks are stopped by the server. Chunks with too much redstone activity will be unable to use redstone signals for a couple of minutes.
The limit is subject to change depending on player feedback and server performance.

Redstone block limits:

There are limits per chunk of how many of a certain block can be placed per chunk.

Pistons: 512
Sticky Pistons: 128
Hopper: 256
Dropper: 256
Dispenser: 256
Observer: 32

Entity limits:

There are limits for mobs per chunk to prevent server and client lagg or crashes. If the limit has been reached mobs won't breed or spawn and if the limit has been exceeded mobs will be removed.

There is a limit of 25 for friendly mobs / animals per chunk.
Large animals have a limit of 10 per chunk.
Animals/friendly mobs with a nametag will not be removed.
Tamed mobs will not be removed

There is a limit of 16 for hostile mobs per chunk.