Xargatha

How does spawning interact with the turn sequence? Specifically, I'm thinking of a niche scenario where Silver Arrow/Xargatha have their anti-movement Blue active, and for whatever reason, are able to cover all available hero spawn points. Do you spawn as part of your action, and can therefore move unrestricted? Or do you spawn, become targeted by those effects, and now have to play under those conditions?

Any change in unit’s position recalculates all active effects.

Would Xargatha next to a heavy minion not gain attack on her primary red? Would this minion still count for reduced defense on an attack?

Immunity has nothing to do with minion modifiers. Only with performing actions.