Q1: Does the On PlayWhen Digivolving effect of this card return 3 cards with "Three Musketeers" in the trait from either hand or trash only onto the deck?
No. Three cards with "Three Musketeers" in their characteristics can be returned to the top of the deck from the hand or trash, or both. For example, three cards from the hand or a combination of one card from the hand and two cards from the trash can be put back on the deck.
Lv.4 Tankmon EX7-043 C Champion | Data | Cyborg [Digivolve] Lv.3 w/[Three Musketeers] in text: Cost 2 [On Play] [When Digivolving] By returning 3 cards with the [Three Musketeers] trait from your hand or trash to the top of the deck, <De-Digivolve 1> 1 of your opponent's Digimon. --- Inherited: <Reboot> (This Digimon also unsuspends in your opponent's unsuspend phase.)
Lv.4 Tankmon EX7-043 C Champion | Data | Cyborg [Digivolve] Lv.3 w/[Three Musketeers] in text: Cost 2 [On Play] [When Digivolving] By returning 3 cards with the [Three Musketeers] trait from your hand or trash to the top of the deck, <De-Digivolve 1> 1 of your opponent's Digimon. --- Inherited: <Reboot> (This Digimon also unsuspends in your opponent's unsuspend phase.)
Lv.4 Tankmon EX7-043 C Champion | Data | Cyborg [Digivolve] Lv.3 w/[Three Musketeers] in text: Cost 2 [On Play] [When Digivolving] By returning 3 cards with the [Three Musketeers] trait from your hand or trash to the top of the deck, <De-Digivolve 1> 1 of your opponent's Digimon. --- Inherited: <Reboot>.
Lv.4 タンクモン EX7-043 C 成熟期 | データ種 | サイボーグ型 「三銃士」の記述があるLv.3:コスト2 【登場時】【進化時】自分の手札/トラッシュから、特徴に「三銃士」を持つカード3枚をデッキの上に戻すことで、相手のデジモン1体を≪退化1≫。 --- Inherited: ≪再起動≫(このデジモンは相手のアクティブフェイズでもアクティブになる)