Is the garage floor lower than the rest of the house? If so, it might be difficult for older people to navigate steps. Just something to keep in mind.

Do you have a rough sketch of the interior plans? Because that will drive your options for door and window placement. Do you want a separate entry for the inlaw suite? For the home office?

Leave the windows as is. Add fixed panel doors in the garage door openings.

I think a garage conversion on a house this size would really negatively impact your resale value unless you build another garage after the conversion. If this isn't a concern for you, then Beverly's idea is attractive. However, I don't see how you're going to get a home office, bedroom and bathroom in a two car garage. Of course I don't know exactly how large your garage is, or how large you were hoping to make these spaces. You really need to consult an architect.

" You really need to consult an architect "

As well as the building dept to make sure the conversion is legal in your area.