You’re right about having to apply for a Regular Commission but you can still be on active duty as a reserve officer, as is the case for most JO’s.
This is not the case anymore, there is no application process to become a Regular Commission. An officer that graduates from any commissioning source is now a Regular Officer once they start AD.
When there’s a RIF, the reserve officers are usually the first to go.
Where you received your commission has no bearing on whether you are subject to a RIF.
Actually all ROTC grads (not sure about academy grads) still typically receive reserve commissions
They commission with a Reserve commission but that changes to a Regular commission once they are activated and start BOLC and AD.