Oh, one more thing but it's unrelated to electrical performance per se. With all that copper, and via stitching, and direct-pour pads, you may find soldering is quite difficult. Especially on those undersized pads for the CMC. Basically the whole board needs to reach soldering temp before anything will melt. And the direct-pour pads have extra surface tension that tends to lift components, leading to tombstoning, particularly when the other pad just has one or two traces leading out of it. (Tombstoning isn't much of a problem for 0805 and larger, but is a concern for smaller chips.) If nothing else, you'll have a hell of a time doing any rework with a soldering iron; hope you have a hot air machine.
2-4 spokes (thermal relief) drops just enough thermal resistance to make soldering a little easier, while having essentially no electrical impact, and for thermal dissipation purposes (at regular component-self-heating power densities) has little effect as well. (That is, because soldering is done with more heat, the temp drop is higher, so the spokes are helpful there, while also being mostly inconsequential in operation.)
5mV is probably in the right ballpark. I'd have to do some calculations to give a better guess.
Note that we still have not resolved whether your power adapter in the first place is the source of noise, nor of what the spectrum looks like (just a forest of spikes, modulated at 50Hz). If it is the adapter, the CMC will at least help a bit, but you may still not observe the noise floor of the board itself, if this is the case.
Tim