Saber cannot resist it. We know this for a fact.
Avalon worked for Saber because you can't curse something that isn't there.
IA is just IA, which you get in general for being an Archer. He doesn't have it as a Caster, for instance. IA doesn't really have an affect on whether someone can curse you, it's whether you can operate independently without support.Gilgamesh resisted it because of rule of cool. He had independent action of A-rank because that was the way to translate his "No one can order the king" attitude.
I don't know what you mean by "main body," especially since Angra literally doesn't have a main body, but that is not the reason he could champ through ego.The mud is not the main body of Angra, so he could take it like a champ thru sheer ego. He was corrupted anyway, though.
Nor was he corrupted.
Yeah, hanging around modern humans for ten years does that to a person.His mind is nowhere near what it was in Zero. He is utterly crazy in FSN.
[citation needed]He is not immune to it, but can resist a lot if the order is not to his pleasing (actually trying to use a command spell at all would already lessen its effectiveness due to him not liking being ordered by lowlifes. Although a clear order might be too much for him to resist.