Q1: Does a digivolution requirement that digivolves from a Tamer mean that the Tamer that will become a digivolution card is treated as a Digimon when it digivolves?

No, it digivolves from the Tamer as-is. It isn't treated as a Digimon that digivolves, therefore "when a Digimon would digivolve" effects and "when a Digimon digivolves" effects don't trigger. In addition, this digivolution requirement can be used to digivolve a Tamer even if a "Digimon can't digivolve" effect activates.

Q2: Is a digivolution bonus draw performed even when a Tamer digivolves?

Yes, you perform a digivolution bonus draw. A digivolution bonus draw is performed for any kind of digivolution.

Q3: If this card digivolves from a Tamer that was played this turn, can it attack in the same turn?

No, it can't. Even if a card digivolves from a card that was placed on the field in the same turn, it can't attack during that turn. It can only attack in the turns after it's played.

Q4: Is a Tamer card placed under a Digimon considered a digivolution card?

Yes, it is. If the Digimon leaves the field, that Tamer is trashed like normal digivolution cards.

Q5: Does a Digimon gain the security effects in the lower text of a Tamer card in its digivolution cards?

No, it does not.

Q6: Does a Digimon gain the inherited effects in the lower text of a Tamer card in its digivolution cards?

Yes, it does.