Does this card’s [When Digivolving] effect force me to trash 1 card in my hand when this card digivolves?
Yes. If possible, you must trash 1 card in your hand for this card’s effect. “Then, you may play 1 purple Level 4 or lower Digimon card from your trash without paying its memory cost” is phrased “you may,” so you can choose whether or not to play a card using the effect.
Can I use this card’s [When Digivolving] effect to trash a purple Level 4 or lower Digimon card in my hand, then play it with this effect?
Yes, you can.
I use this card’s [When Digivolving] effect to trash a card in my hand. Does this card’s [Your Turn] effect trigger?
Yes, it does.
When happens when this card’s [When Digivolving] effect activates while my hand is empty?
You can’t trash a card in your hand, but since you don’t need to trash a card to activate the second part of the effect, you can still play a purple Level 4 or lower Digimon card from your trash without paying its memory cost.