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That new of a card will drop your AAoA. Can't say how many points though. If it was a 6 years old card it would help.
When do you plan on applying again?
I don't understand your question about HPs.
I would first ask the prospective lendor how they view scoring once the info is no longer all yours.
Addition of an AU to your scoring does not permit them, if they so desire, to determine your score absent the account history of another.
They may simply accept the revised score, or they may not. I would ask before potentially creating a situation where they might ask you to remove it.