1) Nope
2) FPSC originally had a very crappy radar system, but it was disabled when it didn't turn out very good. Urlforce enabled it in Lemur Free, though. Other than that, though, you can't do this with a script.
3) You might be able to associate the player with the entity when the script detects that the player is holding down the designated Crouch key. It'd take a lot of tweaking to make it look right, though.
4) If you mean a shield that the player is using as a weapon, then no. Best shield I can think of is an object that the player picks up by right-clicking and holding it in front of them. It wouldn't work against melee enemies, though, considering how they function.
The one and only,
~PlystirE~