Quick Question..
 

How do you know when you need to replace your fuel injections for a n/a? and what kind/type would be good for a 100,000 miles 13b or stick with the stocks one?

Injectors don't generally need to replaced unless there is something physically wrong with them. If the car is getting on in years, then an injector cleaning is a good idea. Most communities have an injection shop that can perform this service. You will need to remove the injectors yourself and bring them in for cleaning.

NAs like low octane fuel.

Injectors spray fuel in a designed pattern. As they age the pattern changes. In the 50 years of servicing vehicles I never found an arbitray injector change to be of benefit. They are most often replace when their solinoid opens or shorts, or if they leak when the engine is off. Leaking will flood the engine and cause hard starting..