Can I use following setup with Windows 10 or do I need Windows Server?
CPU - 1x Intel® Xeon® Gold 6140 Processor
MB - ASUS WS-C621E-SAGE
Windows 10 (Pro, x64) supports 2 sockets with 256 logical cores and up to 512GB RAM, so no problem here.
To be more precise, Windows 10 supports a maximum memory configurations that was formerly available only in the realm of servers:
In general, all Windows 10 editions support a maximum of two physical CPUs, but the number of logical processors or cores varies based on the processor architecture. For example, a maximum of 32 cores is supported in 32-bit versions of Windows 8/10, whereas up to 256 cores are supported in the 64-bit versions.
The Intel® Xeon® Gold 6140 has 18 cores (with 36 Hyper-threading 'cores'), I don't see any CPU-Related problems here.
Sure you can. The only difference is that it was created for server purposes, to been able to run specific apps etc. But you can install regular W10 on this hardware.