Honestly these things are really vital to learn if you want to be self hosting, however if you're unfamiliar with them I would not start with your password vault. You're almost certainly going to make mistakes and risk losing the vault. I would learn on something less vital then once you're feeling more comfortable add vault warden.
CPUbenchmark.net is the best way to compare 2 CPUs.
Directly comparing cores and speed is only useful across the same architecture, comparing brands and different generations should only be done via benchmarks.
I can't provide any feedback about if those CPUs are enough for immich as I do not use it.