I wouldn't have any qualms about having the workpiece overhanging the table.I would make sure the overhang was supported adequately though.The problem is likely to be the very low power turning the cutter.What sort of motor would you expect on the machine?The typical 1/4" trim router has about 600W to work with.The tiny machines may have the facility to move the cutter around your intended design,they may be so deficient in the power that it would take several passes at closely spaced depths to do so.If you get too ambitious there is a real risk of losing steps and chaos and disappointment ensues.As a means of learning the basics of CNC use the little machines serve a purpose and can probably be resold to recoup a good part of the initial cost.You can do a lot of the learning by cutting much softer and cheaper materials than hardwood guitar necks.How much understanding of creating a toolpath do you have?