Similar to the word "furry" a therian doesn't have a universally accepted definition. However, there is some very generalized definitions that can be used.
A furry under a vague definition is "someone who enjoys anthropomorphic art"
Similarly, a therian under a vague definition is "Someone who feels a connection to an animal"
The connection does not have to be physical, it can be mental, spiritual or emotional. People who believe themselves to of been an animal in a past life, and thus feel a connection to said animal, are classified as therians. Therefore, because you feel a mental connection with your fursona (though not a physical one) you are classified as a therian.
While I haven't come to a definition of Otherkin, I have come to some properties that are seemingly accepted to be true of an otherkin.
To be an otherkin you must:
-Believe you are partially or entirely non-human
-You believe you are a mythical creature (such as an elf, dragon, alien, demon, angel and so on)
The second definition I'm still trying to get a straight answer on, however you are probably not otherkin unless you believe you are partly or entirely non-human.
