Hey, thanks for the answer.
1. I don't need all the items from the array in the scene, if that's the question. I only need the items stored in the array for easy access. Also, it's not just game objects for loading, I use arrays to store progress of different quests for example if they are finished - array with 1000 ints, where 1 is finished 0 is not. So to check if quest 3 is finished I go to index 3 of quest-array.
2. Playmakers build in array. Does what I want. I'm working with Unity 2019.4, and because of some other packages cannot upgrade at the moment and when I try to load array maker it gives an error. With higher Unity version it works, but I couldn't see much difference compared to the built-in array, at least not for the purpose I use it.
3. Since I only need to load 2-3 or even 10 cars from the array with prefabs loading the objects in the scene is not taking long. I was more asking if it will affect the performance the way it's making the work in the editor slow when I create an int array with index 1000. Cannot test on build yet as the project is still very rough and even if there is performance loss I wouldn't know if it's from this 1000 index array specifically. That's why I ask in advance if somebody got that figured out yet.

3. I use global, because it's accessible from every FSM not only a specific FSM which is a must have in my case.
Once again to answer "is the gameplay getting slow and/or loading (start playing)" - no I just set the array to be with index of 5000 and Unity hanged so went straight away to the forum to check if I even need to bother further or stick with 99 index arrays.
Thank you for sharing your experience, I will keep try and erroring and see what happens.