There are two ways to spawn bots:
1.) Use script_models
Advantage:
  • It is the cheapest solution, you dont have to rent 64-slots server.

Disadvantage:
  • You have to model and precache every frame of the motion. The max precachable model limit is low.
2.) Or spawn bot players
Advantage:
  • Less server resource needed.
  • Better hitbox.

Disadvantage:
  • It is hard to make good-looking motion.
  • You must restart the server to free the slots.

In the first case I can recommend you my botmod. Download here.
If you choose the player bots, search for meatbot on moddb.
Maybe the best solution if you combine the bot players and the libcod. There are many tutorials on the forum how to use the extension (eg. change player's anim, it may be useful in the future).