Q1: If the 3 cards revealed for this card's On Play effect include only either 1 card with Avian or Bird in any of its traits or 1 card with the Vortex Warriors or LIBERATOR trait, can I just add that 1 card to my hand?
Yes, you can. Even if you only reveal one of the applicable cards, you can still add it to your hand.
Q2: If the 3 cards I reveal from my deck for this card's On Play effect include both a card with Avian or Bird in any of its traits and a card with the Vortex Warriors or LIBERATOR trait, can I choose to only add one of them to my hand, and place the remaining cards at the bottom of my deck?
No, you can't. If you have cards that are targets of this effect, you must add as many cards to your hand as possible.
Lv.3 Pteromon ST18-04 R Rookie | Bird Dragon/LIBERATOR [On Play] Reveal the top 3 cards of your deck. Add 1 card with [Avian] or [Bird] in any of its traits and 1 card with the [Vortex Warriors] or [LIBERATOR] trait among them to the hand. Return the rest to the bottom of the deck. --- Inherited: [Your Turn] This Digimon gets +2000 DP.
Lv.3 Pteromon ST18-04 R Rookie | Data | Bird Dragon/LIBERATOR [On Play] Reveal the top 3 cards of your deck. Add 1 card with [Avian] or [Bird] in any of its traits and 1 card with the [Vortex Warriors] or [LIBERATOR] trait among them to the hand. Return the rest to the bottom of the deck. --- Inherited: [Your Turn] This Digimon gets +2000 DP.
Lv.3 Pteromon ST18-04 R Rookie | Data | Bird Dragon/LIBERATOR [On Play] Reveal the top 3 cards of your deck. Add 1 card with the [Bird] or [Avian] in one of its traits and 1 card with the [Vortex Warriors] or [LIBERATOR] trait among them to the hand. Return the rest to the bottom of the deck. --- Inherited: [Your Turn] This Digimon gets +2000 DP.
Lv.3 プテロモン ST18-04 R 成長期 | データ種 | 鳥竜型/リベレイター 【登場時】自分のデッキの上から3枚オープンする。その中の特徴に「鳥」を含むカード1枚と特徴に「ヴォルテクスウォリアー」/「リベレイター」を持つカード1枚を手札に加える。残りはデッキの下に戻す。 --- Inherited: 【自分のターン】このデジモンをDP+2000。