Q1: I used this card's When Digivolving effect to return an opponent's level 4 Digimon to its owner's hand when my opponent had 7 cards in their hand. My opponent now has 8 cards in their hand, so does the rest of the effect after "Then, if your opponent has 8 or more cards in their hand" also activate?
Yes, it does.
Lv.6 ZeedGarurumon EX4-022 SR Mega | Data | Cyborg [When Digivolving] Return 1 of your opponent's level 4 or lower Digimon to the hand. Then, if they have 8 or more cards in their hand, return 1 of their level 6 or higher Digimon to the hand. [All Turns] [Once Per Turn] When an effect adds cards to your opponent's hand, if you have a Tamer, return 1 of your opponent's level 3 Digimon to the hand.
Lv.6 ZeedGarurumon EX4-022 SR Mega | Data | Cyborg [When Digivolving] Return 1 of your opponent's level 4 or lower Digimon to its owner's hand. Then, if your opponent has 8 or more cards in their hand, return 1 of your opponent's level 6 or higher Digimon to its owner's hand. [All Turns] [Once Per Turn] When an effect adds cards to your opponent's hand, if you have a Tamer in play, return 1 of your opponent's level 3 Digimon to its owner's hand.
Lv.6 ZeedGarurumon EX4-022 SR Mega | Data | Cyborg [When Digivolving] Return 1 of your opponent's level 4 or lower Digimon to its owner's hand. Then, if your opponent has 8 or more cards in their hand, return 1 of your opponent's level 6 or higher Digimon to its owner's hand. [All Turns] [Once Per Turn] When an effect adds cards to your opponent's hand, if you have a Tamer in play, return 1 of your opponent's level 3 Digimon to its owner's hand.
Lv.6 ズィードガルルモン EX4-022 SR 究極体 | データ種 | サイボーグ型 【進化時】Lv.4以下の相手のデジモン1体を手札に戻す。その後、相手の手札が8枚以上なら、Lv.6以上の相手のデジモン1体を手札に戻す。 【お互いのターン】[ターンに1回]相手の手札が効果で増えたとき、自分のテイマーがいるなら、Lv.3の相手のデジモン1体を手札に戻す。