“Swift Gaia the Fierce Knight” and “Gaia the Fierce Knight” are considered 2 separate monsters so you can have 3 of each in your Deck.
You can’t use “Swift Gaia the Fierce Knight” as Fusion Material for “Gaia the Dragon Champion”.
You can use “Swift Gaia the Fierce Knight”’s effect to Summon it (without Tribute) using “Ultimate Offering”.
Your opponent can use “Trap Hole” against “Swift Gaia the Fierce Knight” because it’s a Normal Summon.
You cannot Set “Swift Gaia the Fierce Knight” with “Major Riot”, even if “Swift Gaia the Fierce Knight” is the only card in your hand.
You cannot chain to the effect of “Swift Gaia the Fierce Knight” because it’s treated as a Normal Summon. But you can respond to the Normal Summon just like you would to any other Summon.