As far as build size goes as well. I have built 2 MPCNC’s for myself so far (one for dirty work mill and the other for laser/3d print). I can say both my builds were built around me being able to fit a 20×30″ sheet of foam board under there (with the original intent on being able to cut out rc planes from adams foam board – which I have yet to even attempt). It turns out I have never even cut anything that was more than ~18″ on the x axis and 5″ on y. That said I am printing parts for a third build (luckily I have some extra garage space) which will be smaller (going to mock Ryans build exactly – table and all). I originally thought bigger was better and why limit myself. I like knowing I can throw something quite large under the table but have I really used it yet (no)… So if I were you, think of what material you are going to be throwing on the bed most often and base your build around that. If you are planning on cutting 1/4″ mdf that you source locally in 4’x2′ sections then just allow for the smaller dimension to be able to fit in the bed (you can always over-hang your extra stock.
I am rambling along but I originally thought I ‘needed’ a much larger bed than I have ever really used. Best thing is start small and if you decide you really need a larger table then spend 5 bucks on new conduit – 9 bucks on a 6 pack and spend an afternoon making it bigger. That is truly the beauty of Ryan’s design is it is fairly easy to scale up or down in the future.
happy 2nd b-day mpcnc!