With all due respect to the previous poster...the more aircraft you add...the more system resources they will eat..thus slowing your sim down. So, you will see some performance degradation.
Especially if you use aircraft models that are not GMAX and were not specially designed for use as AI.
If you want more traffic, you need to add models specially designed for that purpose.
You will have to work hard to find a balance between the number of AI you wish to see and how fast you want your sim to run.
Why not visit
www.projectai.com and see what we have to offer.
KJ