the image shown should print perfectly well without supports.
The curves are well within most printers capabilities to print. And sanding blocks/paper are your friend :-)

Can't be arsed to look at the rest :-)

The easy rule of thumb is to draw an imaginary horizontal line from the build plate and move it up. If at any point you have part of the model touching the line that is NOT touching any other part of the model. It needs redesigning or supports.