Are there any major differences between a smaller table band saw and a larger stand up band saw?
From a "size - only" standpoint two critical dimensions of a bandsaw are the throat capacity and the maximum cutting height.  


Throat capacity is the size of the opening between the blade and the frame.  You need your workpiece to be able to fit through this opening as you push it through the blade.
Max cutting height is the maximum amount of blade that can be exposed.  This will impact how many pieces you can stack.  Keep in mind you may not be able to fill the space, depending on the material.  


Larger, more expensive bandsaws will generally have better blade guides, a more powerful motor, more table and fence adjustments, and can hold wider range of blade widths.  Adjustable speed is nice if you intend to cut metal, as slowing the speed will increase blade life.