I doubt the added-on parcel and footprint will comply with your local building code. As others mentioned, consult the building dept, the zoning dept. or the engineering dept.
You can probably consider the closest edge of the sidewalk to be your property limit. If you go online, and use the Building dept. GIS maps, you can see what your zoning district is and then use your online code of ordinances to see what your setbacks are.
I bet your setback is very-close to the minimum now. If you want a bigger garage, the only reasonable option I bet would be to purchase another property which matches your wants.
I used to be a State of FL licensed plans examiner and did zoning/code work, as a planner and other roles.
We did a whole-house renovation before retirement, and fortunately had additional space available. Our answer turned-out to be in the configuration of what you show as your prospective footprint, for the garage. I explored the idea of making the garage two stories, but in 2015, that would have been a minimum of $60 K more, above the cost of the garage renovation, our architect estimated. According to the Consume Price Index, that $60K would be $83K today, probably more.