Star and Steven are tied for best since theyre both nice and both powerful (though Steven is a helluva lot less bloodthirsty he can still hold his own against enemies). They'd most likely become friends, with Steven trying to teach Star to be more kind and think of other ways to solve problems, while Star teaches him to be more upfront and assertive and less afraid to fight.
>Connie fan-girling over Star since her partner is less magical and more human/alien hybrid, making Steven slightly jealous. Connie steals the wand and tries to do spells from her books but they dont work because they're not real. Star uses her scissors to travel dimensions randomly beating people up searching for her wand. Marco finds out Connie took it and tells her its cool to be the normal sidekick, especially since they both can fight without their friends
>Star becoming friends with the Gems and freaking out when she realises Steven and Connie can fuse together. She thinks humans and magical creatures can fuse and spends the whole day trying to fusion dance with Marco. It doesn't work so she forces a fusion with Marco, the Mewman/human hybrid goes berserk and tries to wreck everything. Garnet simply walks over and pulls them apart with her bare hands and gives them the whole "fusion is better with consent" speech.