gnomechild

The long and short of it is, the Mirage F1 has the most realistic implementation of the Aim-9B, J and P seeker heads in DCS. It models a lot of things especially in the 9B that make it particularly hard to use including the inability to uncage it, the seeker null center, and the very limited FOV. Combined with the high aim point (the wingtip missiles center of fov is the very top of the HUD glass) this makes missile employment in the F1 much more challenging than almost any other module. But it is realistic and pretty damn cool from Aerges 

If you look closely at the selective jettison switch you will notice that the middle and upper positions are actually both connected to the "VOL" label as "1" (middle position) and "2" (upper position).

2 jettisons the outer wing pylons and 1 jettisons the inner wing pylons

It uncouples the stick from the autopilot / pre-servo control and switches to the back up direct control. used in case of partial hydraulics failure or autopilot system failure I believe.

Source is F1ED flight manual

#4 MKR + TP is 'Marker' and "telebriefing" (not sure where the P comes in, probably something French. In the manual for the F1ED it's labelled "MKR + TB")
The telebriefing is the ground intercom. If your canopy is closed, you need to depress that dial to talk to the ground crew. The little yellow light underneath it will illuminate when it's active. 
When you're airborne, the dial controls the volume of marker beacons, and the pushbutton does nothing.
For #3, I'm not sure. The dial should control the volume of the RWR, but I'm not sure what the function of its button is. In the F1ED manual it's just a dial labeled "TWR". 

The airbrake is able to be momentary for me. There are three bindings required.

"Airbrake" is momentary
"Airbrake On" locks the switch into position
"Airbrake Off" does what you expect it to

You're correct about GM and Sec.
CM = "cap magnétique"
"Magnetic heading" in English. So in this mode the gyro isn't used by the magnetic monitoring unit to generate heading information for the various systems.

You can hit the C + SW switch while guiding an R.530 with no worries. Your radar will keep lock and continue guiding the missile