This effect means that this card is also treated as a level 6 card while it's flipped over from the deck by a "reveal cards from the deck" effect. If the effect is an effect such as "add 1 level 6 Digimon card from the revealed cards," you can use that effect to add this card to the hand.

Yes, you can. The effect reads "also treated as level 6," therefore this card can be treated as both level 5 and level 6, so you can add 2 copies to your hand.

No, it doesn’t activate.This Digimon is deleted by the rules, not the DP-reducing effect. Therefore, it doesn't meet the "if deleted by an effect" condition.

This effect targets a level 5 or lower card with [Dark Masters] in its text from your trash. This card's inherited effect has been changed to "[When Attacking] [Once Per Turn] By placing 1 level 5 or lower card with [Dark Masters] in its text from your trash as this Digimon's bottom digivolution card, this Digimon gets +2000 DP for the turn." Please see the notices regarding changes to the rules/rulings on the official website.