This is my personal opinion, I would stay at 11 Fire Stations for now and make 3 more EMS Stations, 2 more Police Stations, and make as many hospital beds as you can. If you can I'd buy a coin pack and upgrade your hospital beds easier otherwise you'll have to work your butt off to do this but in the end it's well worth it. Once you have about 15-20 Hospital Beds and more Police and EMS Stations I would work your way up to 15 Fire Stations and stay there then create 2 more EMS Stations.
I would also create at least 3 or 4 cells in each of your Police Stations to keep space in there. In each Police Station I would have 3 Patrol Units and a K-9 Unit. This works for me. Gradually add 1 to 2 more Patrol Units and an extra K-9 Unit as you upgrade your setup.
Hope this helps! Any questions please feel free to ask!
Thanks!
Rescue