Hi! By 6* ticket, you mean that one I guess. (I'm pretty sure there is no other 6* tickets but who knows).
With it, you should definitively pick Dendrobium. She will carry you over 70% of the game by herself. Use her with Ume, Cactus and Angelica Swimsuit and you will have an awesome turn 1 nucker.
Cattleya is good too but you will need Vervain or Roman Chamomile to use her full potential. And they are limited to special gacha. Who knows when it will come back.
I don't know how you got Kerria but she is great. She was top of the top tier in the past. Bigger fishes came in the pond but she is still useable on medium tier missions or on special occasions.
Anyway, welcome here and welcome on the game. Feel free to send friend requests. Having good allies help a lot on early game.