Q1: Can this Digimon attack when I have less than 5 memory?
Yes, it can. Even if this Digimon's attack effect causes your memory to move to 1 or greater on your opponent's side, it doesn't become your opponent's turn until the end of the attack.
Lv.5 MetalGreymon BT1-114 SEC Ultimate | Virus | Cyborg <Security Attack +2> (This Digimon checks 2 additional security cards.)[When Attacking] Lose 5 memory. --- Inherited: [Your Turn] This Digimon gets +3000 DP.
Lv.5 MetalGreymon BT1-114 SEC Ultimate | Virus | Cyborg <Security Attack +2> (This Digimon checks 2 additional security cards.)[When Attacking] Lose 5 memory. --- Inherited: [Your Turn] This Digimon gets +3000 DP.
Lv.5 MetalGreymon BT1-114 SEC Ultimate | Virus | Cyborg <Security A. +2> [When Attacking] Lose 5 memory. --- Inherited: [Your Turn] This Digimon gets +3000 DP.
Lv.5 メタルグレイモン BT1-114 SEC 完全体 | ウィルス種 | サイボーグ型 ≪セキュリティアタック+2≫(このデジモンがチェックするセキュリティの枚数+2)【アタック時】メモリーを-5する。 --- Inherited: 【自分のターン】このデジモンのDPを+3000する。