Epic, Enchanted, and Iconic cards each go into the secret card territory, with numbers that go above the base
Mainly because blue-white (as the preference for at least 2 of the colors for your Commander) don't have that good Voltron commanders to blow the other colors completely out of the waters
Commander, previously (and still in some circles) known as Elder Dragon Highlander, is a popular MTG format in which players use carefully-designed, 100-card singleton decks, headed up by a powerful Commander
Lifegain is often scoffed at in Magic, but incidental lifegain tacked onto interaction does a lot to help control decks get to the late game
If you don't control four or more Birds at that time, the ability won't resolve and none of its effects will happen