Designing for multiple size outputs

Hi,

I need to make a design using graphics, photos and text for output to both A3 and A4.  Before starting the project, do I assume that the resize tool will be the best way if I start using the largest size? And provided I output to the same aspect sizes, this would maintain the photos aspect wiothout distorting.  Or is there a better way?  Appreciate any advice you may have.