The stand looks great, I have some beef with the sump. If you do as you plan, there will be a lot of channeling around the bio media which is not something you want. Also, lava rock is not as porous as you would imagine. Pumice is a much more suitable bio media. I would add some actual baffles to the sump so the water has to flow through the bio media. Your current design will require that the bio media be as tall as the entire sump so that water simple doesn't just flow over the top of it.
I have changed my opinion on baffleless sumps in the past year or so. I do not think they are as effective as a sump with baffles. I can tell you from personal experience that I had issues with my baffleless sump and channeling around the bio media.
I'm not sure what you have planned for plumbing, but you may find your sump to be smaller than you would like if you run a separate pump for your CO2 setup, multiple heaters, a return pump suitable for 200+ gallons, and potential reactors in the future. I know the 1:4, sump:display, is a rule for salt water, but I tend to apply it to my tanks as well.
Good luck! Just some food for thought.
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