Rulings
Q1: If I use this card's Start of Your Main Phase effect to place a card under a Tamer with cards under it, in what order do I place the card?
The card is placed on the bottom of the cards under the Tamer.
Q2: I have 2 copies of this card in the battle area. The Your Turn effects on both copies triggered, and I used the Your Turn effect on the 1st copy of this card to attack. Can I then use the Your Turn effect on the 2nd copy of this card to attack?
No, an attack using the 2nd effect isn't possible. A new attack declaration can't be made during an attack. In this case, the Your Turn effects on both copies trigger, and you use the Your Turn effect on the 1st copy of this card to attack. The 2nd Your Turn effect can be activated before the counter timing, but because you can't declare another attack during an attack, you won't be able to attack using the 2nd effect, even if you activate it.
Data Sources
Taiki Kudo BT21-083 SR General/Xros Heart/Hero [Start of Your Main Phase] By placing 1 Digimon card with the [Xros Heart], [Blue Flare] or [Hero] trait from your hand under this Tamer, <Draw 1> and gain 1 memory. [Your Turn] When your Digimon are played or digivolve, if any of them have the [Xros Heart] or [Hero] trait, by suspending this Tamer, one of them may attack. --- [Security] Play this card without paying the cost.
Taiki Kudo BT21-083 SR General/Xros Heart/Hero [Start of Your Main Phase] By placing 1 Digimon card with the [Xros Heart], [Blue Flare] or [Hero] trait from your hand under this Tamer, <Draw 1> and gain 1 memory. [Your Turn] When your Digimon are played or digivolve, if any of them have the [Xros Heart] or [Hero] trait, by suspending this Tamer, one of them may attack. --- [Security] Play this card without paying the cost.
Taiki Kudo BT21-083 SR General/Xros Heart/Hero [Start of Your Main Phase] By placing 1 Digimon card with the [Xros Heart], [Blue Flare] or [Hero] trait from your hand under this Tamer, <Draw 1> and gain 1 memory. [Your Turn] When your Digimon are played or digivolve, if any of them have the [Xros Heart] or [Hero] trait, by suspending this Tamer, one of them may attack. ---