No prep , in character , standard equipment , winner by KO or surrender
Round 1 - pre time skip
Round 2 - Current
Location - Out Side of Franky House
Both start about 10 feet from each other
Usopp has the advantage in all around stats, but Nami's weapon and her proficiency using it would probably be enough to beat him more times than not, and even if Usopp did manage to get the upper hand or win, he'll regret it as soon as Sanji finds out.