Dui, ni shuo de dui
Ok, no problem at all for cutting foam, actually that’s a great idea for making molds, it never occurred to me.
About the wires, I think it will not add much rigidity. What it will add, is a lot of trouble to make everything square because you’ll have to tighten everything exactly the same. Don’t do this.
Instead, what works really well is to attach your CNC frame to a wall. This way it won’t move at all and it is pretty easy to do.
But since you plan on cutting foam, rigidity shouldn’t be a serious issue, so you can even go without any of those mods and be ok, as long as you set a relatively low acceleration.
(pas de souci, on est pas beaucoup de francais ici de toutes facons…)