More than 2 player co-op (works really well). Also adjust amount of Terrorists in T-Hunt:
First you can keep the bots in a corner and play with your buddies then when a event for the bots is needed they will just teleport once you press the action button of the event which needs them. Afterwards just tell them to get back in their corner. :P
You can play with up to 16 players but that would be overkill. I'd suggest 4-8.
You'll have to make a free account but check out TeknoR6Vegas2 3.0
<-- Only the host will need to do this.
Also a handy GUI to use with it too: http://teknogods.com/phpbb/viewtopic.php?p=32489#p32489
I would also suggest making the bot opponents a bit more rough for the added players. Either using Frosty mod
or Realism Mod
<-- All players will need one of these. (Find a better mod? Post it below.)
The idea is to up the difficulty since the game was designed for 2 people and 2 bots.
For playing online use Evolve
which is a virual LAN program since GameSpy is dead. This is also one of the simplest ways to get matches setup.
However there is also Tunngle or GameRanger. Don't bother with Hamachi.
Hope this helps. :D Ditch those bots and play with real people. :)