My first piece of advice is not to believe everything you read in a book, allow yourself to experience things for a while and draw multiple conclusions. Remain open minded and fluid in your conclusions until you have collected enough data to be fairly solid in your convictions.
In my opinion a spirit has no form per se. It will choose a form which we are capable of perceiving, or perhaps, we give it a form which we are capable of perceiving. I think the latter makes more sense to me.
I dislike categorising beings, I see everything as a spiritual expression be it an angel, archangel, demon, God, Goddess, Fae. It matters not what you call it. I have never heard of a faerie taking the form of a dead person, I don't see how a human dead person could be a faerie myself.
And I don't see how anyone online could have seen a spirit which has been interacting with you.