I think in most scenarios you don't need to worry so much about kvm ram use, since it looks static but actually it's not and you can over-commit [1]. And of course disk allocation can be dynamic as well. I prefer a lot more security for a bit less flexibility. I am not as ram rich as you are, and still every time I think of my few LXCs, my main thought is 'why did I do that?'.
That's true. I know that the dashboard shows the "real" aggregated RAM usage, and truth be told, I'm not particularly utilizing the server to its full extent (I got very lucky, it's a small rack with three PowerEdges, a UPS, 2U Synology box with SSDs, 10 gig switch etc., that I got from a previous employer, and when they found out the cost to ship it all, insured, back across the country when I left them, they looked at the depreciation schedule and said "keep it".
[1] https://docs.redhat.com/en/documentation/red_hat_enterprise_...