Look at statistics of where fires start that cause the most damage and where fires start that kill at www.NFPA.org
Here is a hint....it's NOT the garage.
You are asking for a world of headaches, not to mention that when you go to sell your house someday, a savy real estate agent will ask the...
Use a fire sprinkler contractor. There are hydraulic calculations that are needed and you'll need "dry fire sprinklers" not regular fire sprinklers. Too much to go into but do not DIY.