Ortur makes the machine used in the Donor Machine Video. For the purposes of adapting a Laser Engraver into a CNC Plasma cutter one should prefer a machine fabricated from 2020 2040 or 2060 extrusions so that one can do modifications and affect any repairs that may be needed without being locked into a particular factory. One may be compelled to want to go big by replacing the extrusions with longer ones but one should remember the larger the machine the more difficult it can be to maintain accuracy which is driven by stability which demands more mass generally.  So, my advice is to not modify a machine's width or length until you have your machine operating satisfactorily gaining insights into any gotchyas. One other notable is that a smaller portable machine can be placed on larger pieces of work. The only real limitation is the size of the piece that can be cut out in one operation.