Other parts for an open frame:
A.) Enough power extenders from your PSU to your GPUs.
B.) PCIe risers with power connectors.
You have to basically extend the PCIe slot from the motherboard to the GPU hanging on your open frame.
There are litterally 1000’s of videos on Youtube showing how to build your rig. Take the time to watch some and learn, otherwise you could end up with parts you don’t understand, or missing parts which can make an enjoyable experience quite frustrating.
Start simple!!! If you have (3) 3080 gpus right now, look at them, look at the connectors, read the power requirements. Start from there…
My advice since you’re starting new and have never done this before. Build your system with just one GPU, if you can build it with the GPU installed directly on the motherboard even better. Get your system installed and booted.
Then download and setup up your mining software. Learn how to edit a .bat file and configure your pool settings in your mining .exe. Get it to work. Verify that you are hashing on the mining pool.
If you can make that work then move your parts over to your open frame and add in the PCIe risers and additional GPUs.
As for other parts, nothing special. No need to get an expensive CPU for mining ETH. Find 8GB of compatible RAM and at least a 128GB SSD. Windows is BLOATED and takes up half of that just to install it.