A Dremel with a cut off wheel works well for cutting TIG rod. And then use the same wheel for rounding the edges. If the rod is small 1/8 inch or so, cut half way through and then carefully bend to break. Then finish the edges. Also a Roto Zip will work fine if one needs a little more power. The 1/8 cut off wheels are available at Widget Supply.
http://www.widgetsupply.com/page/WS/...berglass-wheel
For larger mandrels 1/4 or 3/8 a chop saw with an abrasive blade works well on stainless. Clean up the ends with a bench grinder or the Dremel.
There is no magic number of mandrel length. If too short one can use a pin vice to hold. Longer provides the opportunity of making 2 to 4 beads on the same mandrel. But uses up more release. If too short then your hand just gets too close to the flame.