Should I add a Second Home to this Amazing Lot?? Value Add??

[Anton Watt]

Hello BP,

I am planning on buying this home in the Beautiful Kirkwood Neighborhood of Atlanta GA. The home is about 1,300 sq ft and I plan on making it 2,000 sqft after adding on to the home. My ARV for the this property is about $500K after repair. The best part about this property is that the home owner built a 2 car garage/ workshop in the back yard that was made very well and is about 1,200 sqft on its own. I'm thinking of adding a second story to the garage and making it into a garage / spare house. I think this will make the home one of a kind in the neighborhood and add a lot of value. My question to you is do you think this is a good idea and how much value would that add in your opinion? Or do you think I should just leave it as a garage and expand the house as it is. I attached pictures of the garage and the home below. All advice is welcome here!

Thank you