Yes, a creature can adapt again if it no longer has any +1/+1 counters on it , regardless of whether it already adapted earlier that game or not
One CP from each element on the card is always required, even in situations where an effect has reduced the cost to 1
We could easily pick reprints here or note the cards that werent previously Modern-legal, but now are - cards like Shardless Agent and Counterspell are obviously incredibly exciting
Chuckling, giggling, guffawing, snickering, chortling, tittering, shrieking, cackling, sniggering, snorting, smirking, roaring, crowing, howling, cachinnating, screaming, whooping, convulsing, and "yuk-ing it up" all count
If you control a Commander, you even get two effects rather than having to choose