So now that my PC is upgraded I intend to use my old parts to help my brother upgrade his rig. Not as fancy as mine but a good bang for the buck gaming PC. He'll have my old case, psu, gpu, and ram. I think he mostly needs a new mobo, cpu, and cooler. What would you guys say is the best value right now for a new mobo+cpu? Preferably something with longevity that he can upgrade in the future if he wants but is still compatible with my ddr4 ram right now. Bonus if it doesn't need a big cooler as my old case is a bit compact for an ATX.
Well if you are dedicated to using ddr4, you won't really get much in terms of upgradability as far as the cpu goes. I'd just try to get a 5800X3D for $329 + MSI Tomahawk B550 or something similar. Alternatively, you can also get 13600k + Z690 MSI Tomahawk DDR4 version which gives PCI-E Gen 5 for the GPU which costs more however it's also more futureproof. Neither will really allow your brother to have any meaningful upgrades in the future so both platforms are more so set it and forget it sorta deal.
You can also search around for cheaper motherboards, just stay away from Gigabyte and Asrock imo.
PC Specs: CPU: 5950X || GPU: Strix 4090 || RAM: 32GB DDR4 3600 || Main SSD: WD 2TB SN850