I must defer judgement to the person that laid out the ductwork and knows more pertinent information about the project and its location than provided.

There is a saying old as time that go's something like this "Anyone that act's as their own lawyer has a fool for a client". The same could be said of anyone acting as their own GC and cruising the web for help with sub-contractors. If you don't have a trusted support group,get out of general contracting now. If you are paying a GC then second guessing his subs based on advice from the web,you need to stay out of his hair or hire a different GC.

It is hard to tell from this one drawing how the supplies and returns are connected. Is the main supply located in the attic? Are the supply vents 4 feet X 1 inch? If so then why so many and so narrow? I am not used to seeing these type of vents. Is this typical for new builds in Florida?

Are the fours vents at the top supplies or returns? The supplies should be near the big south facing window, and supplies on the east and west wall, with the returns on the north wall.

The 90 degree turn in the main duct needs to be rounded. If it is built as drawn there will be increased air turbulence and noise. If the duct work is in the attic then is should have R-8 insulation.

IMO we cannot answer this ever . As for the sun IMO you needto control it and my go to are solar shades that control heat and UV rays but allow you to keep the view but the HVAC pro is who understands the climate and your home not a bunch of strangers on the internet .

It looks like you have (4) supply registers between the dining table and living seating. That is the sole conditioned air, being pulled into the (4) return registers along the back (South) wall across the living room. Full windows on the West, (2) sliders on the South, (1) slider on the East Dining, and can't tell the Living East wall. It appears to be a reflected ceiling plan and some sort of concrete construction.

The HVAC does not appear that it will provide adequate comfort for this space.

The supplies are slot diffusers which are common in commercial construction and contemporary style homes.

If you'd like to evaluate whether the design is appropriate for the task, I suggest you ask your HVAC designer to review with you the room-by-room cooling loads, duct design (manual D) and the manual T results (air distribution.)