howl hollow howl
1. When a card says you can move a card from an unclaimed flag to any empty spot on your side, I assume this means any place you can play a card and not any flag that has no cards played otherwise these cards would be useless after about the midway point?
That's correct. I originally misinterpreted this as well, but the rules make it clear that "slot" is any position where you can put a card.
2. When you have a leader such as Darius, can you make him a red 8 if a red 8 is already played on the board somewhere?
If the rules don't say otherwise (which they don't), then you can do so.