The somewhat narrow return on L1's garage corner requires framing reinforcement.

The existing foundation and abutting wall structure may prove unreliable for joining to the addition, and must be reviewed by a qualified engineer before construction begins.

The master bath commode is ingeniously tucked away, drained and vented.

There is significant weight concentrated under the zero-clearance fireplace (which can weigh upwards of 600#s .... this one was to have been less), and mud steam shower.  These major loads require carefully-considered ceiling framing on L1 and, possibly, grade beams.

Most of the L2 walls are significantly offset to the L1 walls, arguing further in favor of close attention to L1 ceiling framing plus a truss roof without load-bearing on L2 partitions.

The extraordinary clearspans over the garage (and under the master bedroom) will move the AG to design the L1 garage ceiling and walls with high-stress wood framing techniques more usually applicable to commercial and industrial applications.

Note the details of elevation changes, stair design, schedules, and so forth.

Note, too, the extensive use of abbreviations to keep the drawing open and uncluttered.