That wrasse should be fine in QT, the only reason Howze asked is some species of wrasses you do not want to quarantine (leopards) and some you need some sand as that is what they sleep in.
I think the 10g will be fine for one fish. Did you get the six line yet or is this an upcoming purchase? I would just do my research on them as they can be nasty nasty fish. If you intend on adding any other fish I would hold off, as a six line would be the last fish I would add.