The female disease or whatever it was called was a bullshit way to add gender swap fan service and a shit attempt at a gag. He could have gone with literally anything else but chose that.
Yamato, Momo and Kinemon have the opportunity to join them at sea whenever they want. They have things they want to do before they go so they’re basically like Vivi.
Goku saved his life the first time but a Vegeta did in that fight against Goku. The second time yeah Goku could have won but he chose not to so that’s his own fault.