Multiple answers!
1. Yes, while the base gameplay has cards resolve instantly as you play them, you can use the Start of Turn / End of Turn Card Passives to queue Actions for a specific timing step. May require some additional Eval work to get working but this is possible.
2. Yes, you can use the Deck Editor expansion's new Immutable notetag and Actor Restrictions to make a Decklist exclusive to one Actor. You can also restrict an Actor's card pool used to build Decks by not making the Library shared across all party member.
3. Yes, you can make a card that is a combination of smaller Skill effects from other cards. These could be in the form of multiple attacks.
4. No, effects firing based on gameplay triggers is not yet supported. This will need be achieved with another plugin such as YEP Buff States Core. That plugin is more suited towards creating the windows for triggered effects. You can also conceivably do this via some clever Eval work in Card Actions but we recommend using the other plugin for this purpose.
5. Not yet. This features is coming soon with the CGC v1.7.0 update which is currently scheduled for sometime mid-next year. There is a lot of foundational work that needs to be set up in order to support this system.
Hope that helps :)