I picked the KRUG as a starter simply because it had the fewest screens, is the Dvina really easier to use?

Yes, I would learn these systems in order, First Dvina, then Volhov, Neva, KRUG, Vega.



1 - This seems to light up when all parameters for a launch are met and everything is set up properly.

Manual page 40.
15, “GOTOVN.” Indication shows, that the selected missile, is ready for launch.

2 - This lights up yellow and seems to be linked to the elevation control. Am I right that this is to prevent me from sending missiles below the horizon?

It indicates; Epsilon <= 5 degree.
Just a warning.

3 - This seems to indicate commands being sent from the "Long Track" station, only the yellow warning that the dish is remotely rotated is modeled.

No.
Leftmost, red indication is "PRIN CU" meaning, that the P40 is sending target coordinates, just the SNR is not receiving it.
If you leave the black switch above 1, in the middle accidentally.

Rightmost, green "RV" indication is showing that the K3 command was sent out, radio proxy fuse is armed.

4 - Doesn't seem to be modeled, but what would these lights indicate?

No idea. In the manual I have, that is empty.
Probably a lamp that was used in earlier SNR version, not used with the M3.