Yesss love Kadi! I feel like the other classic 4* yellow aren’t all that great either (I don’t subscribe to the Wu Kong fan club tbh) so considering that you have a good rainbow going with all the other colours, Hu Tao does fill a gap. And I am guessing your raid tier will guarantee that Hu Tao usually lives long enough to do his special on defence, and it’s v annoying to raid against when he does go off. So I don’t think he’s a TERRIBLE choice for a first 4* yellow!
But do I see you have the costumes for Tiburtus and Sonya? Def do those when you can, I use costumed Tiburtus and Sonya all the time.
EDIT: Sorry I missed the second part of your question! Kadi has great defence stats so when you manage to fully ascend her, if your team looks more or less the same, she’s a great tank.
I’d probably do Left to Right… Costumed Tiburtus, Hu Tao (if you decide to ascend him), Kadilen, Sumitomo, Costumed Sonya.
Without costumes, L to R, o.g Sonya, Tiburtus, Kadilen, Sumitomo, Hu Tao… it’s a less optimal setup that way bc it separates Hu and Tiburtus, but I think it’s more important to put o.g Sonya and o.g Tiburtus on the left for the debuff and def down in order before the other three strike.