My M4 pro Mini buying guide:
CPU upgrade, dealers choice. It's an OK value but not a huge perf bump CPU wise.
Storage stay at 512GB and get an external.
RAM stay at 24GB, if you know you need more wait for the Studio Max M4. If you don't know, try out 24GB during Apple's extended return period.
10GbE upgrade see M4 Mini.
Who should buy? M1/M2 Studio Max (M2 Pro, did anyone buy those?) owners who care about CPU over GPU and don't have long running workloads (or don't care about fan noise).