So I take it you want to remake the
look of your house at the same time?
Do you really have the property room per the setbacks to add to the garage side?
An actual photo of the house from the street side would be worth a thousand words right now.
Speaking as an architect, hire an architect.
However, I also do a lot of work with a quality builder I can trust. Some builders only use draftspeople, not all are of equal capability. I have done sketches and studies for people trying to decide whether to move or add on. Typically a meeting with them at the house with a sketch pad gets to to first base.
The first base you are at has opened up more questions than answers. An architect can help you answer those questions by pointing out the positive and negative of each option. However it's still your money and you will have to make the final decisions, although not blindly and not alone.
NOTE:
Start with the site plan and find the buildable area. You can typically get the setbacks over the counter at city hall - smile a lot. Bring your Mortgage Plot Plan/Site Plan, make sure it is to a "scale". Be careful of "breaklines" and other things on the drawing which might not be to scale or might not be accurate.