Yes, both have to be on XX. For example, if text reads "level 4 or lower Digimon card with the [CS] trait or is yellow or black," it refers to a level 4 or lower Digimon card that has the [CS] trait or a level 4 or lower Digimon card that is yellow or black.

Yes, it triggers.

The effects trigger simultaneously, so the player can choose the activation order.

Yes, you can. When this card's DP becomes 0 and it would be deleted by a rule check, its <Evade> and <Decode> will trigger simultaneously. You can activate <Decode>, play a Digimon, activate <Evade>, prevent the deletion, then activate this card's <Decode> again when it would be deleted by the next rule check. If the played Digimon has [On Play] effects, once all processing has been resolved for the rule checks, those [On Play] effects will trigger simultaneously.

Yes, you can.

This effect prevents [When Digivolving] effects on cards from activating. [When Digivolving] effects can no longer activate by triggering or when effects such as "activate that card's [When Digivolving]" effect" activate.

Yes, you can. The effect can activate if it activates upon the [When Attacking] timing.

No, it can't be activated.

No, you can't.

No, it doesn't count. The effect can't activate upon the [When Digivolving] timing, therefore it doesn't count as an instance of that effect's [X Per Turn].