Budget friendly starter build

This is where i hope to document the design and build progress of my CO2 laser cutter. At the time of creating this build it's still in the very early design stages, so bear with me.

What do i want to achieve with this build?
- Comfortly cut 3mm HDF: this will most likely be the main use for this machine.
- Enter the world of DIY CO2 lasers: I have experience with CNC routers already, but lasers are something completely new (and dangerous!)
- Start small, upgrade later: For now, i have no specific need (or room!) for a large / powerful laser, but i would like to keep this an option for if/when i want to upgrade it without having to redesign the build, or have to replace 99% of the components.

Feel free to criticize any and all of my design choices! Always looking to learn from those who have gone before me and learned lessons the hard way.