Ive been using quite a bit of 8" x 3" by 4.8 meter pine c16, Ive been using an orbital sander when sanding.
Would it be quicker easier to invest in a good belt sander?
Belt sander if you want it flat. ROS will follow curves to some extent - smaller and more flexible footprint. So if you've got both you move from one to the other rather like jack plane to smoothing plane. Or miss out the belt if you aren't bothered about flatness. Either way work your way through the grit sizes - don't skimp or it'll take much much longer.