@lucasvinbr
"Hmm, do you think making them always defensive while you control 0 zones be enough?"
Only if I don't start recreating CRASH... that seems sound though, otherwise how would the player be a credible threat? The GTA V storyline? (And that more likely would drive gangs away from the player because come on, who would piss off someone who took on Merryweather and the FIB at once, and won?)

"Or have some sort of "gang heat" that controls their aggressiveness according to your own aggressiveness or something like that"
That sounds interesting. (Wall of text incoming.)
Gangs should probably have relationships between each other. The hostility end should range from neutral to passive-aggressive to dislike to hate to WAR. For each gang war the two gangs come into, the relationship deteriorates by one level. This repairs by one level for every two ticks the gangs do not fight each in gang wars (not ambient fights). Except for "WAR", as cooling down from that requires four ticks of gangs not attacking each other or a peace offering in monetary sum; the latter also resets relationship to "hate" and prevents three ticks from triggering gang wars between the two gangs, ensuring that relationship will fall back to "dislike". Peace offerings can happen at any hostility levels, and is less costly at lower levels; obviously it cannot be used at "neutral".
At "neutral", gangs are neutral to each other, but do plan to start taking over any turf. (Default relationship).
At "passive-aggressive", reprisal attacks are more likely to happen, but gang members do not fight each other by default.
At "dislike", gang members are itching to fight, but are prevented by their leaders. This peace is rather tenuous, however, and gang members could, however unlikely, start fighting each other.
At "hate", gang members are fairly likely to start fighting each other. Their leaders are running out of diplomatic options.
At "WAR", the border turfs of the two gangs will be embroiled in endless battles with reinforcements coming from both sides, and inner turfs are off-limits to hostile gangs. Attacking these turfs require less monetary resources from either side or third parties.
The peace end, on the other hand, should range from neutral to peace to like to respect to alliance. Gangs can declare non-aggression, which improves relationship by one level and prevents gang attacks from each other. From there, gangs can opt to allow gang members on each other's turf and declare defensive pacts. Alliances are reserved to "respect" level, and once that is declared gangs will support any gang attack initiated by one of them on non-parties. This can lead to an eventual, peaceful takeover of one gang by another. Withdrawing from any agreement deteriorates gang relationship by one level (and the agreements must be withdrawn in this order: alliance => defensive pact or open borders => non-aggression), while initiating a gang attack on the other breaks all peace agreements and set gang relationships to "passive-aggressive" and also make the other gang less trusting of the attacking gang.
At "peace", gangs refrain from attacking each other unless one of the gangs is aggressive and it ran out of room to grow. Should the aggressive gang decides to attack, it will give two ticks of advance warning by withdrawing from existing agreements.
At "like", gangs do not attack each other; even aggressive gangs will try to avoid that, and if they do end up planning to, they will give four ticks of advance warning by withdrawing from existing peace agreements. Allowing aggressive gangs to transit the other gang's turf allows the issue to be sidestepped, at least for a while. Gang members may also defend each other, in ambient fights if they are allowed to travel to each other's turf, and in gang attacks if their gangs form defensive pacts.
At "respect", gangs come to each other's aid during a defensive gang war and during ambient fights. They will also be allowed to travel across the turfs. Aggressive gangs rarely plan to attack gangs they respect, and will give eight ticks of advance warning if they plan to do so.
At "alliance", gangs come to each other's aid during any gang war and during ambient fights, and their members can travel across turfs. Aggressive gangs do not plot to attack their allies at all. Wealthier gangs may choose to annex the less wealthy gang later on; if the poorer gang is the player's gang, the player becomes the new leader of the now-enlarged gang. (This could be a viable expansion strategy, in fact...)
Just making gang no longer in perpetual wars can go a long way in adding some dynamics to the mod.
Now that I wrote that wall of text, some personalities should be added to accommodate the suggestion:
Peacemaker: Attempts to improve relations between other gangs. Does have berserk buttons, and does remember.
Gullible: Automatically trusts any gang, unless said gang wronged them too many times...
Fanatical Purifier: Automatically attacks any gang. May lead to frenemies attacking them instead.
Backstabber: Befriends any gang only to betray them later on. Peacemakers can see through them and either avoid them or force total peace and then quickly annexing them, while the gullible will fall to any of the backstabber's machinations unless, of course, the backstabber wronged them too many times. Backstabbers having backstabbers as allies will go to war almost immediately, with predictable results. Do it too many times, and expect frenemy reprisals.

Whew. That came out longer than I expected.