Firefighter for over 10 years and an IT career spanning Red Team/Blue Team and now SRE, I can't recommend enough taking the FEMA Independent Study course in Incident Command.
Even if you don't adopt the system it will help you frame and understand how complex IR can be. Having a scalable system to a) grow with resources and b) grow with external interactions is crucial to have BEFORE you need it.
Specifically, Google's SRE books are particularly useful (https://landing.google.com/sre/books/) along with the book "Incident Management for Operations" (http://shop.oreilly.com/product/0636920036159.do) and Etsy's Debriefing Facilitation Guide (http://extfiles.etsy.com/DebriefingFacilitationGuide.pdf).
The book "Comparative Emergency Management" (https://training.fema.gov/hiedu/aemrc/booksdownload/compemmg...) is also quite interesting, as it compares the emergency management practices of about 30 different countries.