I find Hetzner’s dedicated server offerings to be excellent value for money, and their service is entirely adequate for a box-only hosting provider. I recommend them regularly to anyone who knows their way around a shell.
We (CDCK) run all our stuff on bare metal (via Docker containers, but there’s no virtualisation overhead in containers), because early on we found that both Xen and KVM virtualisation imposed something like a 20% overhead on running Rails apps in VMs – and, since all we’re doing on our boxes is running a multi-tenant hosting environment anyway, the added isolation really wasn’t worth 20% overhead on the apps.
As for exactly how that configuration of box will work, there’s only one way to find out: try it and find out. If that Skylake is the i7-6700K, then that’s the same CPU we use in our machines, and it does the job very nicely. We run more RAM, but that’s mostly because we have a lot of sites so we need more unicorns than a single large site would need for the same amount of traffic.
I really wouldn’t worry too much about not being able to quickly “scale up” your way out of performance problems. At a certain point, almost certainly before you hit the limits of the scale of box you’re describing, you’re doing enough traffic that you want redundancy anyway, and once you’ve got everything setup to use two boxes as webservers, you’ve got everything you need to use 20, if you need 'em. Databases benefit from “scale up” more than app servers, but PostgreSQL will do a lot of work on that sort of hardware, and Hetzner have much bigger boxes you could use for (just) the database if you needed, while keeping a flock of those cheap screamers on hand for scale-out web tier work.