Making my own test bench/open case for PC nerd stuff

I started off by drilling out all the rivets of an old case, I am trying to base my design of the simplistic nature of the open bench https://openbenchtable.com/ just a back plate and the large PCIe card standoffs. My goal for this "case" is to try and reuse anything I have from the original case to avoid stuff I can't do as I lack the skill or tools. I have a budget of practically $0 but a lot of time to spare.

This is what I have done so far.

As you can hopefully see I have cut out the peace that would be above the PCIe standoffs (don't know what they are called so I am going to keep refuting them to that.) along with the top mounted PSU plate with I think a 120mm fan mount that was located above where the IO shield would go.

I was originally planning to keep the I/O shield spot for fanciness, but my long term plan is to get some tooless standoffs from the open bench separately as I really like what you can do with them. With this my thinking was they may be taller then normal so any mobo I put in here will be higher negating the ability to use a shield if the I/O wasn't obstructed in the first place.

The mobo plate as I guess I will call it used to sit on this sheet of metal. At the bottom you should be able to make out some holes where some rivets used to be.

My plan is to cut out this space and reattach it to the bottom of the mobo plate to give it some rigidity as it will help in 3 ways; 1. Is that the holes line up perfectly in 3 of the 4 corners, allowing me to put bolts in for easy attachment. 2. as right now the PCIe standoffs are only held up by 1 axis being the mobo plate. 2 holes are on either side of the standoffs making it so it's very unlikely for me to accidently bend/break off them if attached in this way, aka again better regigity. (like it was made to be and designed that way, who'd a thunk) Lastly, 3. If I attach it this way I figure I can easily hide the screws for some leggs that I would like to attach on the bottom. If for any reason in the future I can unscrew to mobo plate and attach new legs or something.

Legs.
I am not 100% sure how I am going to make them. I do however have the original rubber feet that I would like to use. They could be good for electrical isolation along with that they aren't bad in any way. (idk I also just kinda like them) In the first pic I have and extra peace of metal that was above the PCIe standoffs so maybe I could use that? Or maybe extra metal from the rigidity plate I will cut out. From that piece of metal there is also a significant portion that is bent at a 90 angle so I could possibly cut that out. Also the underside along with the left side is completely black with a matt ish finish. What ever I need it to be a decent distance so the any PSU get's the airflow it needs. Any Ideas or info would be appreciated.

Lastly, or the last thing I can think of what I want to attach. I would like to reattach the PSU bracket on the bottom facing the same direction as the mobo back I/O either right below it or maybe a better spot would be below the PCIe slots. This way if I have that side facing me I have easily access to all ports if I am using it like a test bench. I also possibly have the idea of putting a power button somewhere on that side but I am not concerned about that right now.

Final finish, even though it theredicly would be built at this point I want to make it look decent and not just a bunch of dinged up filled metal. I remember DIY perks talking about how using sandpaper could give the brushed metal appearance and a quick google search looks like it could be a good fit. I don't remember what videos he did this on but if anyone knows the type of sandpaper and technique it would save me the trouble. 

Any and all ideas would be amazing as I would love to hear it. Thanks for checking this out.