vasto lord cant be arracar, they are altedy peak of evolution and alterdy more perfect then arracar (aizen say that)
Vasto lord (unknown how to obtain) > Arracar > Hollow
Shinigami is special race of soul world and use sword can evolve into shikai and bankai, also sword is made from other shinigami soul and can evolve while u connect your soul to the weapon, this weapon fuse with your inner world and tell you name for let u use his power also if u can unlock shinigami lower itself u dont need spiritual weapon
Quincy is special race descend from yawtch and it control your Ability pratically you are slave but if u are strong enought u can break enslavement(only ichigo has do it)
Shinigami can get hollow power and hollow can get shinigami power also if hollow be vasto lord get shinigami power dont need aizen help