There are three kind of warp gates that the AI has -- full, wave-only, and reinforce-only.
A full warp gate is like the actual "warp gate" unit, and that lets the AI both send offensive waves against you as well as reinforce its own planet with new small ships.
Wave-only warp gates can launch offensive waves but don't let the AI bring in more reinforcements.
Reinforcement-only warp gates are like the command stations of the AI, which let them bring in more ships but not launch offensive waves.
The number of each kind of warp gate is irrelevant: as long as the AI has at least one that allows waves, if can launch offensive waves. And ditto for the reinforce-only ones.
The only way to stop all reinforcements is to kill the command station, since it is a reinforce-only warp gate, but killing the command station doesn't guarantee that reinforcements will stop since some other units (like warp gates and special forces guard posts) also allow for reinforcements in.
Having more warp gates of either sort does NOT increase the potency or frequency of waves or reinforcements. All it does is provide redundancy to the AI, so that if you destroy one such thing they don't lose their warp capacity.
Hope that helps, and welcome to the forums!