Garage conversions are always problematic.
You are juggling great immediate need, versus use of the house, Code compliance, HOA compliance, then the like.
Then, there is "fit." A two-car garage is too big for a single bedroom, and lop-sided after adding a full bathroom. Single-car garage is too small, even after adding a closet.
Cities tend to be tough on these, as the sequence of 'extra room" to "mother-in-law apartment" to for-profit rent space is too easy to make--especially at the time scale municipal planning and development rules need to work within.
The fact that you need electrical, mechanical, and plumbing changes--and permits for all that--further complicates the issue.
Toss in the access/egress needs for a bedroom space(s), and it gets even dicier.
Which is where spaces like home-theater or home gym, are better conversions. That is, after one copes with the way garages are often very low-ceilinged for their widths & lengths.
For a temporary solution, I'd probably be inclined to build a floor up on sleepers, and to stand separate interior walls to the dimensions needed of the spaces required. treat them all like a "temporary" building with in the garage space. This could allow retaining the existing external features of the garage. And would make the "de-conversion" a simple one of demolition of partitions.