Will leaky fuel injectors cause the car difficult to start when engine is hot and backfire when accelerate? Thanks in advance.

I think backfire is due to unburnt fuel which a fuel leak can cause. Leak injectors can also cause flooding, which can happen when engine is cold. If your engine is shut off after driving (hot) and injectors leak while you park, you may have difficulty in starting.

Fuel leak should be addressed prompty even if it's internal. If you are leaking, you should be running rich. Plugs can be soiled, start up can be smoky. It could be a fuel pulsation damper leak also which can cause engine fire.