Oil temperature for flavor extraction?
Depends on the oil, when we infuse like to think of it as steeping not boiling or heating to the point of just below the smoke point as the spices will cook and not infuse, some will also become bitter. I also suggest you put your chilis in all at once or toward the end of the infusion process if you are layering the flavor or want a less intense flavor. Also are your oils for dressings or for cooking? If they are for dressings they will keep their integrity when your process is finished, heating or cooking the oil will alter the taste you may be aiming for. Two different animals. Lastly I personally prefer grape seed or light olive oil for infusing.

Cheers!

EDG