The logic board is not designed to support that much power.
Think of it this way… You plug into a single outlet two large space heaters the current load will cause the outlet and the house wiring to over heat, it might even set the house on fire!
So in your case as you load up your system there is nothing stopping you from going to far.
I would recommend you find 2012 MacPro in the long haul it will be cheaper and you might even get a better system! Or one that can support what you want.