Iroas's last ability prevents all damage dealt to attacking creatures you control, not just combat damage.

The type-changing ability that can make the God not be a creature functions only on the battlefield. It's always a creature card in other zones, regardless of your devotion to its color.

If a God enters the battlefield, your devotion to its color (including the mana symbols in the mana cost of the God itself) will determine if a creature entered the battlefield or not, for abilities that trigger whenever a creature enters the battlefield.

If a God stops being a creature, it loses the type creature and all creature subtypes. It continues to be a legendary enchantment.

The abilities of Gods function as long as they're on the battlefield, regardless of whether they're creatures.

If a God is attacking or blocking and it stops being a creature, it will be removed from combat.

If a God is dealt damage, then stops being a creature, then becomes a creature again later in the same turn, the damage will still be marked on it. This is also true for any effects that were affecting the God when it was originally a creature. (Note that in most cases, the damage marked on the God won't matter because it has indestructible.)

Your devotion to two colors is equal to the number of mana symbols that are the first color, the second color, or both colors among the mana costs of permanents you control. Specifically, a hybrid mana symbol counts only once toward your devotion to its two colors. For example, if the only nonland permanents you control are Pharika, God of Affliction and Golgari Guildmage (whose mana cost is {B/G}{B/G}), your devotion to black and green is four.

Numeric mana symbols (, , and so on) in mana costs of permanents you control don't count toward your devotion to any color.

Mana symbols in the text boxes of permanents you control don't count toward your devotion to any color.

Hybrid mana symbols, monocolored hybrid mana symbols, and Phyrexian mana symbols do count toward your devotion to their color(s).