Yeah it's crucial to get over 10 chain value here. Hit with luffy last then, even if his last tap is also lvl 1 he will deal more damage as he is boosted on this kizuna
unfortunately she's the most crucial character in this particular team, try searching for other teams, there are plenty of excellent optc content creators who have suggested other teams
I don't think there is one, but you can farm the Franky, it's a f2p character. Just have to unlock his arena quest in the recollection archive and clear 2/3 runs
You can try with legend perona but you will have to be under 80% of your max hp somehow, so if that's not possible then I don't know who could replace her sorry
psy tm f2p chopper will work fine. You can buy him for blue tickets in the tm shop in case you don't own him yet. The support is just here for stat improvements so it's easily replaceable