Avoid hyperthreading CPU’s (or turn off in BIOS) with RouterOS as it causes weird issues.
If you use a 5+ release my experience : The more cores the better the performance whilst older ones releases seemed to favor higher clock speeds.
Xeon will smash a Celeron from what I recall in my tests.
Do not buy cheap garbage machines with crappy realtek nics.
YOU GONNA HAVE A BAD TIME
Stay with enterprise hardware as it tends to be a more stable and long term platform.