Hello! Late pledges are closed on the Kickstarter but don't worry I'll have plenty to sell directly after fulfilment.
1. Yep. If I understand your question correctly, page 3 of the current rulebook (v6.1) covers this here:
Note: you can spend multiple values on a single hero to pay for a conquest. Example: if my Champion has 2 x pools of 2 resolve, I can spend both of these to play a 4-cost conquest.
2. Interesting! In your specific situation with Chains of the Divine, I'd say choosing to banish 0 is acceptable, because of the wording "up to 3". The card's first floor ability however, "Banish the top card of the deck", requires you to banish.