Biggest problem for single player campaign at least what i think is "story" along with maps.
I am interested, how would you write story for sp campaign? What would it be about? How many maps would be there? How would be save function worked (Save/Quicksave ~ Load/Quickload) or would it be based on checkpoint (somebody like that, somebody don't ~~ it's more matter of taste). Would you insert/add more alien models? ... (common stuff like that)

RTCW had great story and 32 map cycle along with it (btw. ai was separated in script (map).ai file).
In that script you could edit everything player & bot related.
this is one example
//
player
{
spawn
{
cvar g_episode 6
accum 0 set 0
accum 1 set 0
objectivesneeded 2
mu_fade 0 1000
mu_queue sound\music\x_atmos
}
...
//and for enemy
venom1
{
attributes
{
starting_health 150
aim_accuracy 0.5
aggression 1.0
camper 1.0
}
...
EDIT: Current bots in Quake3/Tremulous suck donkey balls, and without scripting system, you cannot set individual bot anything related to single player.