I worked at a clothing factory, and in order to enlarge the sewing area (especially helpful for quilting large items as quilts and keeping sewing supplies close) ... the factory took 3/4" plywood width of the table x two feet or more, attached 1x4 or 1x6 border around three sides, making sure that the 1 bys extended along the depth of your sewing table (or depth - - front to back). The "arms" were screwed into the table. Then, underneath, to stablilize the addtional "table" 1 bys on each side, extending over the table and addition. (Just thought you might appreciate the extra working space) Another suggestion I learned a few years back had to do with placing your sewing machine in a corner of the room, so that you face the wall, the extension is against the wall to your left, thus using the wall to help you control the quilt.
Congratulations on your new table, it is a DANDY!