For #1, it doesn’t seem right to me for immunity to be equivalent to “attackers of this target cannot deal damage.” Are there any hero abilities in DE that specify a number of targets to deal damage to, but without a “you may?” Wording like: “Hero deals 2 targets 1 projectile damage,” such as EE Harpy’s Uncontrollable Flock. (I think Absolute Zero First Appearance, iirc?) The reason I bring up that situation is, suppose the only non-hero targets in play are Baron Blade and Mobile Defense Platform. After hitting the platform, the hero would have to choose a hero target for the next instance of damage, if your interpretation is correct, instead of picking the Baron and watching the damage fizzle. That just doesn’t seem thematically right to me.
I guess your question for #2 really boils down to: is the order static effects on all cards in the order they entered play, followed by regular effects on all cards in the order they entered play, then optional effects on all cards in the order they entered play – or is the order static, regular, and then optional effects on the first card to enter play, then static, regular, and then optional effects on the second card to enter play, and so on?