Hoop size limits the embroidery area. It ranges from 10 centimeters square to 24 by 15 centimeters, and prices increase accordingly. You'll need mobility to fix broken threads. The best machines allow free movement to any position, but some limit the correction range to eight stitches. If you like to improvise, get a machine that lets you override automatic settings or select certain portions.
Some models can alter stitch density and design scale.