Like the others ... where you are will determine some of what you will do.
Be sure to factor in all the seasons, and weather changes ... and the effects they will create for the short term while you are in there, and the long term, such as humidity and dampness potentially creating mold.
Another factor to check ... any bylaws and/or regulations for you to make the changes you want. That might determine whether the garage door could be removed and a patio door installed. That being said ... you could always leave the garage door, and open it on nice days. Screening might be a good consideration as well.
There is so much more that is do-able ... you really need to think it all thru as to what your needs and wants are. You can get so many ideas from the previous threads where others have shown their sewing areas and what they have done. Make your wish list and do some graph paper work, to determine the layouts and how things might fit in.
Have FUN as you make your plans and see it come into being!