Q1: My opponent activated this card's On Play When Digivolving effect. If my Digimon without digivolution cards then gains digivolution cards by digivolving or other method, can it now attack?
Yes, it can now attack. This card's On Play When Digivolving effect targets "none of their Digimon with no digivolution cards," therefore Digimon that no longer meet the conditions can no longer be effect targets.
Lv.6 Cthyllamon LM-006 C Mega | Virus | Fairy [Trash] [Main] By returning 1 of your Tamers to the bottom of the deck, play this card with the play cost reduced by the play cost of the returned Tamer. [On Play] [When Digivolving] Trash the bottom 3 digivolution cards of 1 of your opponent's Digimon. Then, until the end of their turn, none of their Digimon with no digivolution cards can attack.
Lv.6 Cthyllamon LM-006 C Mega | Virus | Fairy [Trash] [Main] By returning 1 of your Tamers to the bottom of the deck, play this card with the play cost reduced by the play cost of the returned Tamer. [On Play] [When Digivolving] Trash the bottom 3 digivolution cards of 1 of your opponent's Digimon. Then, until the end of their turn, none of their Digimon with no digivolution cards can attack.
Lv.6 Cthyllamon LM-006 C Mega | Virus | Fairy [Trash] [Main] By returning 1 of your Tamers to the bottom of the deck, play this card with the play cost reduced by the play cost of the returned Tamer. [On Play] [When Digivolving] Trash the bottom 3 digivolution cards of 1 of your opponent's Digimon. Then, until the end of their turn, none of their Digimon with no digivolution cards can attack.
Lv.6 クティーラモン LM-006 C 究極体 | ウィルス種 | 妖精型 [トラッシュ]【メイン】自分のテイマー1体をデッキの下に戻すことで、このカードを、戻したテイマーの登場コスト分、支払う登場コストをマイナスして登場させる。 【登場時】【進化時】相手のデジモン1体の進化元を下から3枚破棄する。その後、相手のターン終了まで、進化元を持たない相手のデジモン全てはアタックできない。