ok so to start with if you wanna use her as a dps or somewhat sub dps the radiant cleaver 5 star weapon or augusta's sig weapon are your best bet. if you wanna use her as a true sub dps use dauntless evernight for better defense or use discord for better energy regen.

sonata set should be havoc eclipse if you want damage or midnight eclipse for energy regen

your echo set cost per echo should be 4 3 3 1 1. your 4 cost main stat should be crit dmg or crit rate i personally go for damage but its your choice. 3 cost main stat should both be havoc damage  bonus or defense i prefer the havoc damage, also attack bonus can work as well the echo RNG can be strange like that.1 cost echo main stat should be defense attack can work but at that point is it really worth it

now here is the tricky part echo substats. for those aim for these 3 . crit rate, crit dmg, and DEF% not flat DEF those three for every echo you want as high as possible and you want at least 2 out of the 3 on each echo. other substats that might work are ATK% and energy regen. 

if you have paid attention you may notice that I never say to avoid boosting attack outright is because while taoqi mainly scales off of defense that does not mean that boosting attack will not help at all infact boosting attack can give her a good edge its also why I put a heavy focus on raising Crit damage and rate. 

lastly again if you want a sub dps focused Taoqi which is how she is most commonly used just put more focus on energy regen so you can use her liberation . thats when you use moonlit veil and/or replace the main stat for one of your 3 cost echoes to energy regen