I believe the inspection must be done by a shop on the list unless you live in another region.
M rated helmets are designed for a single impact, whereas sa is designed for multiple impacts. If you roll your car you will probably have multiple head impacts. It is not uncommon for a car involved in an accident to hit a wall more than once (say rear then front). That being said accidents at DEs are not that common. Regarding the fire extinguisher, I bleieve you are allowed to attend one DE without an extinguisher btw.
Enjoy your weekend on the 15th!