not really any hard and fast rules. I've run all sorts of combinations and its all pretty close. emulator pin can help with some minor latency and audio hiccups. But many think that the more cpus you add the more emulator pins you should have. I just watch and if the pin(s) i'm using are maxing out, I add more. It seems really dependent on the type of workload.
I don't know if unraild allocates the ram as "take all from one side(cpu) first" or "take from all sides(cpus) equally" allocation method. I've never run into any memory speed issues though using 2-4 procs, with ram on 1-4 processors so i've never looked into it. This isn't solid info, but just my experience. The equipment I run was used for running way more vm's than I do and it managed that fine. So I imagine that running a single vm doesn't stress it in terms of ram access. But I wouldnt mind being proven wrong and being shown better optimization that actually makes more than a 1% difference.
your emulator pin assignments of 2, 24, 46, 68 in the xml are boxed/identified as in your unraid grouping, with the emulator pin box 3, 25, 47, 69 having nothing assigned to them. So thats why you are seeing activity as you described.