1) Talking about whether something “enters the battlefield as a creature” can be confusing, because it conflates two different questions with two different answers–which replacement effects are applied to an object that is entering the battlefield, and which abilities trigger as a result of that object entering the battlefield. I'll cover the latter here, since that seems to be what you're concerned about.
In order to determine what abilities trigger when something enters the battlefield, you look at the very first moment after that object has entered the battlefield to see if that object, as it exists at that moment, matches the conditions of any ETB triggers, those abilities trigger. All three cases you mention here will trigger
Aura Shards, because in the very first moment after it has entered the battlefield, it is a creature–there is never a time when the object has already entered the battlefield, but is not yet a creature.
2) The Starfield and the God do not have the same timestamp, because if multiple objects would receive a timestamp simultaneously (for example, when
Replenish returns multiple enchantments), the active player determines their timestamp order relative to each other. (CR 613.6j)
If the active player chooses to give the God the earlier timestamp, then the Starfield's animation ability will always apply last, so no matter what the God will always be a creature with P/T equal to its CMC.
If, on the other hand, the active player chooses to give the Starfield the earlier timestamp, the God's “de-animation” ability is applied last, so whether or not the God is a creature at any given moment will depend on whether or not its controller has sufficient devotion at that time. While it's a creature, though, it will always have P/T equal to its CMC.