So as stated in this post https://gamejolt.com/p/hey-guys-i-have-the-boss-orders-in-mind-so-1-fb-01-2-cancerous-3-w-ygcqurxu I have got the boss list order but here's some updates

1 FB-01 will be the "tutorial" boss so you'll fight him near the VERY beginning of the game

2 White Pegasus Red Torus and Green Dragon order is "wrong" because you can fight anyone in any order (but White Pegasus will be the first in the Boss rush) so technically there's no "canon" one to fight first (but the recommended order will be to start with Red Torus)

3 Booette/Heart Force Shining Star will NOT fight Andromeda Bloopy in the story mode and in the Boss rush mode she will fight Black Bloopy instead (to keep things consistent)

4 Aries and Andromeda Bloopy can be fought in any order