The main differeces are in the number of Central Processing Unit (CPU) cores, the amount of memory (RAM) and as a consequence the type of motherboards.
Depending on CPU types and the number of CPU cores the CPU socket (with which a CPU is connected to the motherboard) could be different and not all motherboards can take all CPUs.
For example if you wish to have a 10 core CPU for each workstation within your DEXTER personal cluster, this determins the size and type of the motherboard because a 10-core CPU can only be installed on an ATX-size motherboard. This motherboard is one size bigger than an mATX (micro-ATX) format and provides more features, more connectors (USB, network, etc.) than its smaller counterpart.
So the first thing we recommend for you to decide is the number of CPU cores because this determins a lot of other components.