Not sure what the third CS aircraft is. I suspect you might mean the modified Lear45 (mine is CS_FA-18), plus these two:
CS_intruders
CS_intruders_heavy

Those last two are AI aircraft only. You can see them by flying in different places and, I think, in different years. You encounter the different period AI aircraft by doing that. I have only flown around by adding Weapon to my Wings of Power II - Spitfire Mk IA and shooting AI aircraft down around local airports. I have also flown the F-4 at 12 o'clock.FLT that was also installed with Weapon for FSX.

As to the 2D hud - it is Weapon Control Panel opened using Shift+1, the HUD Glass opened using SHIFT+3 and the HUD itself using SHIFT+2.  Those are the default shortcuts for them in my FA-18, I'm not 100% sure about the Lear45.

In the Menu (ALT > View > Instruments) you should look for
Weapon Control Panel
HUD Glass
HUD.

Mark