Does equipping an equipment to Irelia Fervent count as choosing? For example, equipping Guardian Angel to Irelia, would that give +3 Might total this turn?

Yes, equipping Guardian Angel to Irelia, Fervent counts as "choosing" her, and it will trigger her ability to gain +1 Might.

According to RiftJudge FAQ #9143 and #6203, equipping gear to Irelia, Fervent is considered "choosing" or "targeting" her, which satisfies the condition of her ability: "When you choose or ready me, give me +1 Might this turn."

Regarding your total Might calculation:

1. Triggered Ability: When you pay the cost to Equip Guardian Angel to Irelia, her ability triggers because she has been "chosen," granting her +1 Might.
2. Card Effect: Guardian Angel itself provides a static bonus of +1 Might to the unit it is attached to.

In total, Irelia, Fervent will receive +2 Might (the +1 from her ability and the +1 from the Guardian Angel gear), not +3 Might.