to redeem Merrill+ points for airline tickets

1) do you go through a Merrill+ portal to book the flight ticket? or do you transfer the Merrill+ points to airline first? FT posts from past few years indicate the latter but i dont understand how that is supposed to work - i presume it goes into a diff account from the FF account you collect your airline miles?

2) Per DoC, AA/BA/DL/UA supposedly allow you to redeem 25,000 points for up to $500 in flights (2¢ in value), while all other airlines allow you to redeem 30,000 points for up to $500 in flights (1.67¢ in value). Would it be possible to book a flight via one of these airline websites (AA/BA/DL/UA) but that, the flight booked is actually operated by their partners?

3) Minimum redemption is 25,000 or 30,000 points (or up to $500 worth in flights). Does it mean $500 = 1 flight, or will it also work if $500 = multiple number of flights?

thanks in advance for any tips